How cool is that? This is what made me fall in love with RetroArch. Now, all you need to do is switch between different emulators to play your chosen games.
Install as many emulators as you want (albeit the ones supported by RetroArch) and then load your gaming ROMs. What will you do? Technically, you will close the emulator for GBA games and then fire up another emulator for Nintendo games. For instance, you may want to play GBA games and then switch to playing Nintendo 3DS games.
Essentially, it eliminates the need to install different emulators for different games.