The big supermarkets in the UK have a "scan as you shop" system. There is a portable scanner you take along with the trolley and scan each item as you put it in the trolley (directly into a bag - avoiding the bagging step).

You then just go to the self-checkout and pay for what you scanned.

They do spot checks at the checkout, especially for "new" customers. It's tied to your identity (need to scan a store card to unlock the scanner).

I think it's a timesaver... even though it takes a bit of time to scan each item with the portable scanner, you get to skip the "unload from trolley -> scan -> load into bags" at the checkout.