Like Bwammo said, limping, especially open limping, in general is usually not a good idea. I have seen plenty of solid SNG players who like to limp early in the game from early position with small to mid pocket pairs. Essentially they are trying to see a cheap flop and set mine, since hitting a set in SNGs is a great way to double up. Also, early in the game, it is certainly ok to limp behind in position with hands that can flop big (pocket pairs, suited broadways, suited aces) when there are 2+ players in front of you who have already limped. But remember, in these pots, especially with a hand like Ax suited, your goal is to flop a big hand, not just top pair, as you will find yourself in some trouble with top pair-bad kicker, in a multi way pot. However, once you hit the middle game, there should be no more limping, as raising, isolating, and stealing blinds will be the more optimal play
But another thing to think about as to why you should not be open limping is because you do not give anyone else a chance to make a mistake. Other's mistakes equal more chips for you. If you limp and its folded around to the big blind, he gets a free flop. You are not giving him a chance to make a mistake. By raising, now players have to make a decision to fold, call, or raise. Any one of those could be a mistake that you can profit from depending on their hand and position.
One player in particular that I have helped with their SNG play had the habit of limping into a lot of pots and just leaking chips 20, 50, 100 at a time. Taking the extreme route, I said for the next week, you are not allowed to limp into any more pots. You either raise or fold. Needless to say he said that this has already helped his game as he is reaching the middle and late game with more chips. So long story short, limping has its place, but you will do just fine if you eliminated it from your game.