It depends on how "awful" the limper is and how he plays postflop IMO. He may be the worst player in the world and have limped with 72 offsuit, but if you can't get him off a K 7 3 flop, what's the point? I will only limp in this situation if the players in front of me are passive and easy to steal from postflop. Playing for a set right here is a waste of chips.