Fist of all, Horrible defender, doesn't run an offense, combo guard stuck in between two positions - who does that remind you of ???? FIIIIIIISH!!!
That's why I don't want him.
Second, regarding fields. That scenario is only possible if NY signs JR Smith, which is looks like they might. In that case, Fields would be stuck as a third SG (behind Shumpert and JR) or behind Melo at the 3. Thus, there is a good chance, that NY would let him go this summer in order to adress a few more pressing needs (backup 4 and 5). Barnes would be a really nice fit in NY behind Melo as a tough energy guy behind Melo. Also he can play the 4 at times if needed.
Second two-guard. Shumpert will be the backup PG. Shump has been playing more PG than SG this season (according to minutes), and while Jeremy Lin is a nice offensive player, the Knicks will need a defensive-minded PG, and that's where Shumpert will stand out the most in the playoffs (especially against Rondo, Rose and Cole).
Baron Davis is close to retirement. I wouldn't put any money on him returning to last year's form (which was still bad).
Fields will back up JR Smith at the two, and get minutes at the three as well. Douglas or Balkman are out of the picture, which helps significantly.