There may be a thread for this topic already but I haven’t seen one so I apologize if this is redundant.
I’m just now getting back into the game and this time on Xbox one, after a few weeks I’m finally about to get to 72.
It’s been a grind for sure so my question is this: what are the reasons for moving to the OP levels? Is it more fun or challenge? Is there more content or levels you can’t do at 72?
Many thanks
In my experience, climbing the OP levels was more about having tougher enemies. The reward is stronger gear, yes, but constantly facing very challenging enemies can get very tiresome and frustrating. And despite having reached OP8, I still regularly play at OP0 (regular 72) because it’s just right for me. I try to balance my gear so I’m not walking around in god-mode just blowing things away. It’s more of a casual pace that I control with what guns I use, what skills I use, and what my goal is foe that session.
A guy on here will use lower OP level guns and such on higher levels making it like a customizable difficulty slider. (Like using OP3 gear ONLY while playing on OP6 or something like that…)
It’s for the additional challenge. Once you hit 72, I’d recommend you stay there for a while, tinker with your gear and build, see what you like. When 72 doesn’t offer you as much of a challenge anymore, then perhaps you could start trying out the OP levels.
There’s no risk with the OP levels (other than if you haven’t bought it and it turns out that you don’t like them): try a run up Digistruct Peak. If you don’t make it, who cares? You’re still sitting at 72. If you do make it, you have the option of playing at OP1, but can still choose 72. Try it again: die? Who cares. Make it? OP2 is an option, but you can still choose 72.
The OP levels can be used to tailor game difficulty and buff weapons, but at the end of the day, if you get to OP8 and that whole ride was a whole lot of nope, you can just choose to play at OP0 (which is level 72).
Both Ninja_Mrrr and farsight37 make some great points, if you want “the” end game challenge that’s what you get with the Peak. You don’t decide to play at higher OP levels, you earn them and this can take some time and effort in acquiring the necessary gear as you gain OP levels just to keep pace with enemy health re-gen.
Having said that once you do obtain higher OP levels, or even if you choose to at all, i’d say play around at higher levels and find out where you feel comfortable. You can adjust the OP slider as it were to make you stronger, or the game harder by keeping lower level gear and fighting higher OP leveled enemies which can be lots of fun, is possible and can improve you as a player also.
The game stays the same, there is no new content you will miss out on by staying at 72, so don’t worry about that, just a change in enemy toughness and gear with higher stats to use at your disposal.
Personally i love the challenge of the Peak and if you haven’t been there this guide by @Handsome_Dad will give you a great insight into the Peak, what to expect as you make your way hopefully through higher OP levels.
There is a link to @Jefe 's guide on elements at the Peak which is also very useful if you are not sure as well.
I hope this helps you out and if you do have a go at the Peak, i wish you good luck and make sure you have fun as it can be very testing at times and you may need to just take a break from it and get back to normal old Pandora for a while, but it is well worth a try i believe. 
Digistruct Peak is a huge grind for me and I would recommend doing it in coop if you can. I’ve had some misguided concepts of prowess at various points and tried to solo it but it was misery, especially as Krieg.
Getting to OP8 is worth it though - for the reasons Adabiviak says. Being able to select enemy and weapon level gives you unprecedented control over how difficult you want the game to be and what guns you want to use. OP8 is also fun for me because there are lots of great coop players hanging out there!
Adabiviak has a really good way to do it.
You set your level @ Op 3/4 , then tailor the level of the gear to bring everything into balance.
For example , powerful guns like the Harold would be dropped down to say 72 , whilst underwhelming guns ( Veritas) would be OP 7/8.
This way you dont god mode yourself and alot more gear becomes viable.
There are plenty of folks here that have ungodly hours into the game that cap at 72.
For others with ungodly hours ( or even not ungodly ), going to the Peak is simply taking advantage of more content. But you’re not missing out on anything other than Peak experience if you avoid OP : you can still get all the pearls ( 
) if you own the DLC and I can’t think of anything else OP offers other than what the others have stated.
I do specific levels per character : some at OP8 because that’s best for me ; some at OP4 or OP6 because any higher is just too hard.
I moved to OP levels because I usually try to beat the games I play at their hardest difficulty, otherwise it feels like I left something undone.
If there weren’t OP levels and you could stop getting experience at will, would you quit leveling at, let’s say, 69 or would you keep going to 72 anyway?
It’s completely personal preference to get OP lvls or not. I’ve stayed at different OP lvls at a period each, to feel what’s the balance between me, my enemies, and the loot. I can say if you want balance just between you and the enemies, OP3-5 is the right level to go. Lower than that is even easier. Getting to OP8 increases certain drop rate (Tubby will drop more pearls in OP8 than in OP0, and coincidentally the only gear I haven’t got to drop is the Bekah), but it also doesn’t let me to beat every single raid solo with every single class. For the latter, I don’t mind, I have my brother to help my raids, so it’s OP8 all the way for me. As for other enemies, I’m sure raids are the highest peak of enemies here, so if I can beat some of them, I have no problem with the lower tier ones.
Also, mobs in DP is much harder so, prepare yourself should you decide to go in. However you will find it refreshing to mob in normal areas in the same OP level just after you beat DP since they’re easier. The difficulty will surely go up again when you try raids.
I have dug the information myself from developer’s console (UCP requires this to be unlocked). OP0 has Tubby pearl drop rate at 1%, and OP8 at 20%. While the OP8 one seems to be very high, combined with the chance of seeing a Tubby, it makes sense. I also made sure not to run any mod which affects drop rate (UVHM+ mod does this to vending machines and world drop but actually it uses Tubby pearl drop rate as a base, which means it increases on every OP level without a lot of work).
I can give you screenshots or text from dump files in the next hour or two, only if you want.
Brilliant - thanks for that! Don’t worry about digging for screenshots, that info’s great.
That’s strictly for the tubby drop rate? And not OMG? I heard something somewhere about something along those lines, but it only applied to OMG…
OMGWTH has guaranteed pearl on OP8, that’s it I believe. I never dig anything about it. Maybe I can dig something… if I know where to go 
Also, I think world drop rate is increased too but I’m not too sure. I ony have dug information about Tubbies.
Nocturni posted the same - I’m quite certain the sliding scale only applies to tubby drops.
I’m curious about random pearls from chests and piles, etc if the % increases.
That might be more of challenge to find.
Ye, I think gen2 pearls have a stupid low drop rate at OP0 and it goes up the higher you go in OP levels. I never knew this before TheHunt2017 during which multiple streamers had trouble getting them and there was a collective realization they need to start climbing the peak if they want those points for the pearls.
I did it because it was one of the biggest challenges available in the game, and I’m big on pushing myself. I insisted on doing it solo because I wanted to prove to me that I earned it. I also enjoy talking about things I love, but I have a strict personal rule against speaking with conviction without having first hand experience and understanding. In order for me to offer advice with Zero, for example, I knew I needed to earn the ability to speak from a place of “been there, done that, learned this”.
I take a mixed approach. I didn’t go to the Peak immediately after hitting 72, but did so fairly soon after picking up the level 72 quest rewards I’d been waiting for. However so far I’ve only gone to OP3. The Peak is a lot of fun (you have to do it at least once, just to see the Combat Garden!) but I find it has diminishing rewards. My gear is already perfectly fine at 72; being able to get non-quest-reward gear one level higher per run is nice but not a big deal to me. And every run is a bit harder, plus they’re one-life runs by construction, so there’s an element of pressure that’s not present elsewhere in the game. Since I don’t have a lot of time to play, and am generally pretty tired when I do play, I transitioned to gradually leveling up my other characters rather than pushing Maya to OP8. I’ll probably get there someday, but it’s not a priority.
My first character to his OP8 was, of course, Gaige. I put in tireless hours grinding to 72. I was also quite a newbie to the Borderlands universe so my build was shaky, my gear was everywhere, and the concept of quest rewards and farming will all but foreign to me. Shortly after hitting 72, I and a couple of old gamer buddies, hit the Peak and I managed to claw my way to OP3 with them. Got stuck there for a while and connected to a guy offering free weapons at any level. I did some research, worked out my build a bit, and figured out what weapons I wanted.
Instead of just getting them however, I ignorantly accepted his offer to “instant boost” me to OP8 so he could give me what I asked for at that level. It was nice, until I tried playing at OP8. Talk about utter, miserable failure. For the longest time I hid in 72 because I wasn’t good. If I played with others who were on higher levels, I ended up almost as a dead weight.
A little more time passed and I researched and learned as much as I could. Once I felt it to be enough, I gradually began increasing my level of play until I was confidently mobbing at OP8 solo. (Peak is another monster) It was good experience to do the OP levels rather than just bypass. Its not just about having strong stuff, but having real in-game experience that I use now to be a better player. And thanks to that whole experience; I’m now an opposed party to instant levelling just to get powerful gear and say you have reached the highest level. (There are exceptions of course and as always I don’t condemn anyone who prefers it. To each his own. Just as long as we are all having fun)
But even now, I prefer playing OP0-OP4 on most days. It can challenge me still, but not to the point of rage quitting with wild fury.