Main issue I have is that my current campaign is more of an exercise in character interaction than a classic PnP campaign. Sure, we do have fights and missions (it's military themed), but more often than not my preparation involved figuring out how to get each individual player character motivated to undertake said mission. That said, I do have a long-term game plan in place, a metaplot if you will, and a billion NPCs will run that metaplot even if the PCs decide to be involved in other ways than those I can think of ahead of time. The world does not revolve around my PCs by default, but they are certainly in a position to make it if they want.