Premiere edits After Effects does not.
After Effects is effectively photoshop for motion graphics. It allows you to stack up layers like you would with a .psd file and apply affects to them and turn them on and off. Premiere can acheive this to a certain extent, but After Effects is capable of using the photshop blend modes [colour dodge etc etc] and applying animated effects to layers, and many other things which Premiere cannot do.
Essentially the two are designed to work together, Premiere first to do the editing then After Effects [hence the word "after"] to do the clever stuff.
Premiere renders at a higher quality than After Effects and After Effects is not designed to deal with hours of footage, it wants you to give it small segments to play with... it will deal with however much footage you throw at it, but you'd better have a fast machine if you import 30 mins into it.
It's not commonly used professionally for films,because truth be told it's a bit clunky, however it is more widely used in making commercials. The only film I know of which was post processed by After Effects is "Sky Captain and the World of Tommorrow" starring Jude Law, Gwynet Paltrow and Angelina Jolie.
