Limping small pairs in tourneys
You really do not want to be doing a lot of limping in tourneys.
If have a hand like 33 and you want to open limp it(be the first to limp) or you are over limping(limping after others have limped) you want to make sure that the stack sizes of the players that are or could be in the hand are at least 30 big blinds.
You need to have stacks this deep to make it worth while the times you hit your set. If you have 33 and limp with 10 blinds and have to fold it really hurts your future chances in the tourney.
When you limp instead of raise you are giving up fold equity(the value of getting your opponents to fold), initiative(making an action that suggests you have the best hand), and the power of position(the ability to act after your opponents, where you have the most information- given you have seen how your opponents have played).
There is an exception to the 30 big blind rule -when you have less than 10 big blinds and have Aces. Then you can limp and call off trying to maximize the amount of chips you will win.