No difference in how it performs in Poser. External .obj is handier, though, and it is also required by DAZ (and, I believe, Renderosity) for brokered products. Not sure what their reasoning is, but I like that you can make changes to the geometry or mapping without having to re-save the prop. Also can be cute to address the same external geometry with more than one pp2; in my old set I had a couple of swords that had two smart-prop files; one smart-propped to waist/scabard, the other smart-propped to hand. Both props used the same geometry file. Oh, yeah, and for some stuff it's nice that Bryce or Vue user can use the prop without having to go through Poser. Of course these days more and more applications are opening Poser files native...