Like almost every other play in poker, whether to limp or not depends a lot on the tale dynamics and the situation. I will limp in the big hand in early position if I am at a table of over agrressive players. If I feel pretty confident someone else will raise, I'll limp in ealry position and go for the check raise. If I'm at a table with a lot of calling stations, passive players, or players who like to see flops for cheap, I'll raise every big hand I get. It all depends on the players and the situation.