The benefit of doing a massive, comprehensive amount of "prep." While I absolutely agree that this kind of world interaction is excellent and something DM's should strive for, in practice it's often hard to do. Planning a whole encounter might take significant prep. Letting the players bypass it with a check or two, that can be hard to swallow. And it also implies the DM should be sitting on 10 times more content than what's going to come up at any given time.