Ah, ok - simplistic example:
Imagine that we open KsKd utg at 4xbb and get called by btn, blinds fold, so the pot is 9.5bb's. Flop is Th9c6h.
At 40bb's starting effective stacks (36bb's remaining), we're very happy to pot the flop (say 9bb's, 25bb's now remaining) and call all in if btn raises. We don't really care that the flop is wet, our stack to pot ratio dictates that we're ok w getting it in.
At 100bb's starting effective stacks (96bb's remaining), we're less thrilled w this flop (depending on villain types). If we bet 9bb's (87bb's behind) and get raised, we're going to have to decide how many draws are in villain's range and what our equity is against those ranges if he raises. Getting all in on the flop isn't a concern - we're probably not going to shove over a raise in this spot, so there's too much behind to get all in on the flop - but we do have to worry about turn cards, we're out of position, etc.
At 200bb's starting effective stacks (196bb's remaining), we're even less thrilled. There's too much money behind for us to be excited with this flop for our hand. That's not to say that we're necessarily folding to a raise, but we have to be thinking ahead and deciding how much money we're willing to commit out of position with lots of horrible cards that could show up on the turn and river, and we have to think about how btn will be playing the hand (for example, is he going to bet any flush/straight card that hits the turn regardless of his actual hand) and whether we can realistically take this hand to the river.