Ak

[Penguinfan]

I have always brought in AK for a raise simply to eliminate A/rag K/rag hands that may catch their kicker if I let them in the pot and then you are losing a big pot with a flop like K-7-8 if you let the guy with K8 in the hand. Depending on how he plays it you are gonna get drug along for the whole ride and left shaking your head because you are not getting off AK with that flop.
You are on the other end of if by limping with 78s, you are looking to win a big pot from someone with AA or AK if you can, and if you miss the flop altogether you can easily dump it costing you 1 small bet, but can easily win a huge pot with a flop of K-7-8.

Lose small pots, win the big one.