Pros for slowplaying AA/KK preflop (by slowplaying I mean flat calling a raise or 3 bet):
-Helps you mix up your game, keeps you less predictable and balances your range;
-People behind you might try to squeeze you , in which case you get go over the top;
-Lets you get away from the hand cheaply if the board becomes very dangerous and heavy action is developing;
- Allows you to trap poor postflop players who just can't get away from top pair but would fold their hand a lot of the time you reraise preflop.
Cons for slowplaying AA/KK preflop:
- Gives the preflop aggressor free cards to draw out on you;
- Keeps you from putting as much money as you can in the pot when you're certain you're a big favorite;
- Entices calls behind you, which reduces your equity in the pot;
- Doesn't give you much information about your opponent's range.
I probably left out important details because this is a fast analysis, like discussing stack sizes, but by comparing the two options you reach a conclusion - you really don't need to slowplay these hands against weak players, because they won't be paying attention to how you play, will call your reraise everytime with any cards worth raising for them and more players will certainly call as well behind you, creating a multiway pot you do not want. So, against bad players, don't slowplay. Against good players, sure, you should do it once in a while to vary your game a bit. Hope this helps...