So in theory, you might one day edit the images of an XFL file directly in Photoshop without disturbing the timeline information also contained in that file. Or you might be able to import a page from a word processing document into a Flash presentation.
I regularly hear people claim, incorrectly, that to use ActionScript 3.0, you have to know object-oriented programming, or every variable's datatype must be declared, or everything has to be in packages and classes.