Robti
If the screw is tight , nothing !!
If its not you risk moving the collar whilst adjusting grind. Apart from changing the number this will scratch the body as the grub screw is pointy. ☝🏼
As a side note my body was pristine (the grinder body, obviously not actually my body!!) when it arrived so i never fitted the collar at all as it was as near as required to zero with the printed numbers on the body