It happens to me over and over again that I need to free up multiple slots in my inventory (e.g. to make some margin for mass dismantle) but I don't want to get rid of any particular material in it - I just want to discard e.g. half of my concrete, or all but four stacks of iron plates. Doing so is rather tedious at the moment as I have to drag every single stack at a time to the trash can, or drop the stacks I want to keep on the ground, then Ctrl-trash the rest and then pick the dropped ones up again. In all cases it involves complex dragging and dropping operation with the mouse.
I suggest adding ability to select multiple stacks in the inventory, e.g. through Shift+Click, then drag/drop them all at once. Ability to select stacks this way could also allow deleting them by pressing the Delete key (perhaps followed by Enter for confirmation) as an option beside dragging them to the trash can.
While I miss this mostly for deleting, I believe it could be also useful for transferring items to/from storages or for dropping items on the ground.