I'm no expert on AE -- still definitely consider myself to be in the process of learning it and picking up new ways to apply it in vidding as I go. Thus far, I've used it for opening titles, ripple effects (the effect controls were a lot more precise than what Premiere had to offer) and speed ramping (when you want to be able to vary the rate of speed of a clip over time, rather than just doing a flat percentage speed change).