I know this is read dependant, but against unknowns...
You raise in position with AK/AQ and get a couple callers. The flop comes out with 3 unders (rainbow) and one guy pots it ahead of you. Do you bother calling or reraising?

What if:
a) two suited unders
b) two connectors
c) other caller ahead of you

Think about how much your hand can improve to make this worthwhile. If you spike an Ace, are you ahead or will that cost you more?