If the would be transfer is larger than the fee, and there is not enough left in the balance to cover for the fee, to request to subtract what more is needed to cover for the fee from the would be transfer.

This way if someone wants to transfer their entire balance somewhere else, they can without accounting for the amount that should be left to cover for the fee.

(I understand that there are pull requests that make the transfer process more convenient, so what I'm suggesting here might already be implemented, but then again, it might not. I at least don't think it is.)