Let's say i owe someone 5 coins. I hand them to him one at a time. Does he acquire each one as i hand it to him, or does he get all of them after all 5 are in his hand? When exactly does ownership get transferred?
The proposed nafka mina (practical difference): One of us drops a coin in transit, and it gets lost. If he has already taken possession of it, i shouldn't have to give a replacement. But if the coin still belongs to me, i'd have to give another one.
(This is just an example. CYLOR if it happens to you.)