because Gl can support a lot more features, reason to have more than 2 UV's is for things like masking where you may have a lightmap, mask, and 2-3 layers of mulltitexturing. you often want to have entirely independent mapping on each layer to give you the most flexibiliity with things like terrains.
Wy restrict yourself unless the games complexity demands it. more than 2 UV's will allow you a pretty big hike in graphics quality, probably about 40%, and also cut down on the number of textures you need. So despite the extra UV channels slowing things down and using up extra vram, you will most likely save a lot by cutting back on surfaces, and get cleaner transitions between textures.
Wy restrict yourself unless the games complexity demands it. more than 2 UV's will allow you a pretty big hike in graphics quality, probably about 40%, and also cut down on the number of textures you need. So despite the extra UV channels slowing things down and using up extra vram, you will most likely save a lot by cutting back on surfaces, and get cleaner transitions between textures.