If its the pocket twos we are talking about.. otherwise this is a weird subject.
I usually limp with them or fold them if Im facing a big bet pre-flop. Chances for hitting a set is the same as with aces kings and so on, but the difference is that if you make a raise people tend to put you on a big
hands, rather than pocket 2s and they think they have you beaten with a pair of aces.
If nobody raises,, or he raises small, its worth to get into the pot, but when the numbers are too high you might want to skip that.