I think with assisted passing the pass always "snaps" onto a player/target, regardless of aim. If you miss the first target somehow, it'll try to snap onto the next player. I like to call it "magnetized". Even 1 bar pass support does this. The pass has little error regarding the passing player's body gesture/stance/orientation, and the receiving player goes to the ball regardless of the passing angle, even if it is a mis-pass.
With 0 assistance, the receiving player spends more time "looking for the arriving ball".
The difference is especially apparent when you play one-touch passing. On 0 assistance, each subsequent one-touch has less and less reliable accuracy (since receiving player is always looking for the ball, and thus not in a right body orientation to send a perfect one-touch for the next pass). This can be solved combining one-touch with 2, 3 touches.
I guess. Something like that.