From the Readme: "" Why use obj files instead of putting the geometry information in the prop file? -Less memory intensive: when you add another copy of the prop to the scene, Poser only has to reference one obj file. -When you save a scene file, Poser saves the reference to the obj file rather than saving the geometry information. -obj files can be imported into other programs, pp2 files can not. -Some marketplace sites require that prop files reference external obj files.""