Shift clicking a stack will send the 64 stack to the top of the inventory instead of a chest or furnace, etc. This leaves the stack separated and you having to inconveniently reach for the rest of the stack to continue its proper placement. (Apologies if this is duped!)

Edit: If there is an incomplete stack at the top of the inventory and shift click a full stack (like in the hotbar) to put it in the chest/furnace, the stack separates and joins other incomplete stacks at the top of your inventory instead of going into the chest/furnace.