I think you belive customers like self check-outs. I do not believe that to be true. I hate self checkouts. I will stand in line for 15 minutes with 4 items before going through an open self check-out.
However most stores by me have mandatory delays after every item as it weighs your bagged of scanned items to make sure you didn't slip something you didn't scan in there. It painfully slows down the process even the times where it doesn't misfire.