I've been limping a lot more lately for a couple of reasons.
1st - if I'm in early position and I want to play cards that aren't super premium (I don't consider AK to be super premium when played from EP) I will limp to see how much resistance I'm up against. I fully expect to be raised, but the question remains by how much and by how many players. I don't want to get into a dominated and/or Bingo situation with a lot of my money in the middle out of position, so if there's a lot of resistance I can just fold having only sacrificed one BB. However, if there's very little resistance, say a standard raiser and a second limp/caller then I really want to see the flop (for cheap).
At the lower limits I've lost far too many
hands by automatically raising my better playable hands pre-flop only to be called by two or more random hands that hit a lucky flop and/or turn.
2nd - if I'm betting into a super aggressive pre-flop raiser, or habitual 3/4-bettor, I want to maintain some pot control before I see the flop. If I know I'm going to be raised regardless of what I do, I would generally prefer to keep villain's raise to the minimum pre-flop (e.g., 3X vs. 9X or more).
That said, I will play super premium hands (AA, KK, less often QQ, and cautiously JJ) super aggressively pre-flop if the table will permit. I expect to win with these hands, and want to narrow the field down to only one villain so that my dominating
odds hold up better.
However, if I'm at a really tight passive table, then I will usually raise every hand that I want to play regardless of position.
And finally, if I'm short in a tournament (which eventually always seems to happen) then I will try to force through my less than premium hands when I think I may have a shot at doubling up. I'm trying to rely on fold-
equity here, but most players are going to call shorter stacks with their medium/better quality hands in those situations. I hate full-ring tables because there are almost always better hands out there.