The only good thing about hi-caps is that a lot of guns come with them, so you can play with the gun without needed to buy a ton of mags right away.
I've had my G36 for 3 years now, and have used it's hicap twice -once right after I got, and once more against a team who only used highcaps and pretended they each had fire hoses.
Other than milsim games, most people won't care if you have a highcap, though there are a few things you should be aware of:
1) They rattle and make noise and are a pain in the arse to wind.
2) Many games put an ammo restriction. They'll say like 'max 400 rounds on you'. So if your highcap holds 470 rounds, you can only put 400 in it, and only have one.
3) If you're using a highcap and don't execute proper trigger control, like short, controlled bursts, you'll lose a lot of people's respect very quick. There's few things in airsoft I hate more than people hosing with highcaps like they have a machine gun. In fact, this is one reason I discourage new players from using them if possible. They don't force you to control your ammo usage and encourage the "spray and pray" mentality of gaming.
4) Reloading under fire is totally fun. Seriously, you have no idea how much fun it is to be in a firefight, run out of rounds, be like "fuck.." and have to swap mags while taking fire. I think people who only use highcaps rob themselves of that fun.
5) Like was mentioned above, most mil-sim games don't allow highcaps at all -mostly for reason number 3 stated above. People are willing to accept that not everyone has realcaps... but there's a big difference between 50-100 rounds in a mag and 300.
"Someone in a Prius tried to race me at a stop sign the other day. I couldn't believe it. I had him for the first 100 feet or so but I can only walk so fast."