If you plan just use the full set through standalone emulator, the split set (default) it's a better option storage wise, you can learn about it here: deleted the torrent because it was broken, and to enforce the to generate a new one, it seems to be fixed you're using retroarch, you better follow this archive:

Games depend on the BIOS and parents ROMs in order to work, the full merged non set make each ROM zip file contain all files needed, so each game works independently, it's a better option for the people that want just a couple of specific games or that uses frontends that have troubles to locate the ROMs dependencies, the major drown back it's that requires more storage space.