I doubt you would notice anything, it just causes wear on the belt and sprockets as the belt is tensioned and un-tensioned a small amount every time there is a difference in speed between engine and wheel.
A cush drive is just a form of shock adsorber that is found, mostly, in the transmission when a belt of chain is the final link. Some cars have shock adsorbers in the transmission, often in the form of rubber cushioned universal joints of some form.
