Well if you move your model around a lot then render it will get very ugly and pixelated, according to the Lynda.com video, that is because Photoshop is destructively resizing the map interactively.  I've seen it myself when I did a lot of transforms on a model, it won't be pretty for close ups--trast me on this one.  I think that moving the camera, rather than the models can accomplish similar results without the degradation problem.