I understood that Sainsbury's had trialled that and it was a resounding failure, customers deserted that store in droves.
It also assumes that people are just shopping in basket loads, not trolley loads. I hate those self service tills if I have more than about 4 items. They cannot cope with customers having light cloth bags where for the first 5 or 6 items you tend to pick it up by the handle and shake it open to put items in. It ends up coming off the weighing worktop, the bell goes and you have to wait for staff, explain the problem and get them to hold the bag open while the first few items go in - and do that as many times as youhave cloth bags.
Then what happens when, like me, you do a monthly shop and approach the till with a trolley load of stuff. Now a days I unload it all on to the belt, put all my trolley bags in the trolley and load directly into the trolley. A this wouldcause two problems at a self service till 1) No space to unload, the goods will not go on the weigh out surface.