The purposes of raising are...
1. Get more money in the pot now while you may have the best hand... your opponent may not put any more in after the flop.
2. To get an idea of what your opponents are holding... so when the flop comes 356 you can be fairly sure he doesn't have 47.
3. To make your opponents think you have a good hand... they're far more likely to fold to a continuation bet if you raised big preflop and they caught only a little piece then if you limped along.
4. To narrow the field... with a good hand that is likely to be the best, it's always better to play against one or two opponents instead of giving your opponents cheap odds to hit a big hand. It's also easier to take down the pot without showing cards.
5. Finally... to force your opponent to make a mistake by calling you with poor odds. This increases your EV, and is always nice
200 is probably enough to accomplish most of those goals... but a bigger raise will be better for the first four goals but not the last one. I'd prefer to make a raise on the small end of the scale you mentioned... I don't mind hands like suited aces or connectors staying around since I'll win the money they put in far more often then they win what's allready in there. Personal preference though... with a lot of money allready in the pot I'd raise a lot more since I'd like to get that cash right now. But that's not the case here.