Your question is a lil confusing, whe you say "what's the difference between using the MPC for drums opposed to the digi002" do you mean as opposed to sequencing in Pro Tools?
Well, either way, I tend to do all the hardware sequencing(drums, samples,Triton Extreme, sound modules)on the MPC and sequence Sampletank, MinimmogV and Reason in PT. I almost always start with drums so I just track the drums into PT and just start adding layers as I go, goin back and forth between hadrware an software sequencing until I feel the song is done, then everything gets tracked or bounced to audio in PT.