Usually the value of a small pocket pair in no limit hold ‘em comes from the possibility of making three of a kind (called a set) on the flop and winning a big pot. So, if you're facing a raise before the flop and you're holding, say, 55, you need to think about the amount that you're going to get paid off if you flop a set. If the opponent is very tight before the flop, and only would raise QQ-AA and maybe AK, that's a great position for you, as long as the stacks are pretty deep compared to the blinds. Because then if you do flop a set, there will be a good chance the opponent has a big pair and will put a lot of chips in the pot.
On the other hand, if your opponent is going to be raising a wide range, you can't call with the intention to give up every time you don't flop a set, because you won't get paid off enough when you do. In no limit poker, sets will be what you use to win huge pots.
