I use emulators mainly for NES, SNES, GBA and DS. I use the first 3 because where am I going to find a new game for those today, where the money goes to the company? I use the DS emulator mainly as a way to test out games to see if they're worth buying, hell most of the DS games I own I bought after trying them on an emulator. I also use it to play games that are hard to find, case in point Monster Rancher DS, I have never seen a copy (new or used) in any store since it's release.