Actually it brings up plenty "problems" with instant transfers aswell. The minimum period of Transfer Listing of three days offers up alot of Gameplay strategic Values - your opponents might see him, you have to take into calulaction if and when he leaves, what happens if he doesn´t and so on.
An instant sale option without the 3 day time makes some things in franchise planning alot different and alters the whole roster management situation. It´s not only a minor chance, but a pretty big one you have to count into any "pro / contra" situation.
Zwei Dinge sind unendlich, die Dummheit und das All...