Do you have any extra compressors? Reverb units? Guitar Pedals? Filters? Ring Modulation effects?
This is some of the many uses you may find yourself trying with the multi-outs for your mpc. You don't need to do this of course, but if you want to try to experiment and see what it can do to your sounds, you'll probably find something dope to use, and possibly give a little bit of oompf to your sounds. You can find guitar pedals or sometimes rackmount effects in pawn shops, or music stores. Sometimes they're cheap, and having a few around is sometimes cool to use on synths, or for making some distorted bassline or crunchy drum beats.
Just some of the uses for your multi outs...