limping in NL Holdem is not too bad during very early levels of blinds and from good positions. But as soon as the blinds get to a good level, raising pre flop or folding are really the best two options. I see so many players continue to limp in from early positions when the blinds are high, then have to fold when someone raises. Remember, if your hand is good enough to play at all, then you should bring it in for a raise. If you hold something like 6-6 and raise then the flop comes 6-4-2 you must be in front.....if you limp in, 5-3 off suit is just the sort of junk the BB will be holding and will probably bust you !
In limit your raise can't be large enough to force out all or most players pre flop so limping in is more common and you have to play more flops, turns etc. Bluffing is also very tough as a call on the end with a reasonable holding will often be the value play due to pot odds.