I almost always shoot product photos against a green screen. This allows me to quickly and accurately cut the product out from its background and then use it in any number of ways. For what I do - tricking the eye is vital. If I was to stack a dozen guitars one in front of the other - if shot from say, 6-7 o'clock - there would be an unavoidable issue with perspective. Regardless the lens used, they can't all occupy the same plane from that angle. So the guitars in the back will be smaller - because they are farther away. If I shot them individually and put them together - that would eliminate the issue of perspective, but your mind would immediately recognize that something was wrong with the image. This is where PS is such an amazing tool. You put each on its own layer, stacking them the way they'd be stacked in reality if you were shooting them in a studio, and you add a supplemental layer between. I use Alien Skin/Black Box - Eye Candy for PS. A powerful series of plugins. I can program a drop shadow that simulates a real lighting and shadow environment for the guitars and by creating these little variations in shadows and highlights, you can trick the eye into thinking it is seeing something real. In the first, third, and fourth photos in this card, these guitars were all shot separately and added to a composite image in PS. Regarding backgrounds, or with green screen work, the "plate" - I create most specifically for the image in question. I have an extensive library I've created now. You'll note that in several of my cards, "I Am Aries", "Send Me An Angel", etc... they share the same plate.