I put a crusher top of my Drawer and I always have 1024 iron/gold dust, so I don't need to wait crusher work when I want to craft something need dust.
But if I use AE2 or RS to autocrafting something, I usually craft more than Drawers limits and drawers would empty and put another things inside, and my automation broke down.
So if there is a upgrade that it will make drawers got empty but show 0 item not Nothing, autocrafting would just wait crusher.

This is what the "drawer key" does. You don't even need to spend an upgrade slot on it.