then you'd in essence be sending a copy of the ffl back to the ffl holder.
the ffl copy is only so the sender knows that they're sending to a valid ffl holder, otherwise any joe could give their address and say "this is my ffl guy" or whatsoever.
if you're talking about the seller's FFL needing to send HIS license, it wouldn't be a bad idea, that way the shop can keep it on file for future reference.