Development; developing standalone execuitables is easy, but for an emu you need to load in roms and all that; so you need an SMC, and shipping the emu to your GP32 device to debug is a slow cumbersome thing. With GeePee32 you fcan have a virtual SMC, and thus you can fire it up for debugging and stuff nearly instantly... saves *mucho* time
Virtual SMCs are "images" of smart media cards for GeePee32. You use it for like, if you were testing Frodo, you can launch Frodo with GeePee32 but to load a game it's going to look for an SM card for the games.