well i sync my 2000xl to my VS1680 and i think midi syncing isnt that necisary into a recorder, but it just makes everything a little easier. Here are some things i'm able to do because i sync them....
-i got a 2000xl with only 2mb memory, so until i upgrade, i'll fill all the pads with some sounds, make a beat, record the beat into my VS while its synced up to midi. then i'll save the MPC sounds, erase them, and put a whole new disk of sounds on the pads. then i can play back the previosly recorded data from the VS and overdub more drums/samples using the MPC, and both will be in time together....you could do all that without using midi, but the midi just makes it easier.
-just being able to see the measures and beats of the drum track once its recorded into the VS. I have people rap over all my beats, so its nice to be able to see all the measures once its recorded into the VS....that also goes for recording a live bass (or any instrument) over the mix. Its not necisarry, but its helpful.
-I havent done this, a friend of mine has. i told him to try it, and he got it to work....once i got all the tracks on my VS filled with beats, instruments, and vocals, i'll try to put all those 16 tracks of data into pro tools (also as 16 seperate tracks). He'll run a chord into the comp via midi, and also the RCA monitor cables (red/white). Then sync up the midi time codes and solo one of the 16 tracks, play it, and record it into the computer. Then solo a different track, record it...until all 16 tracks are 16 new tracks in pro tools.