[0]: https://upload.wikimedia.org/wikipedia/commons/1/13/Barcode-...
[0]: https://upload.wikimedia.org/wikipedia/commons/1/13/Barcode-...
Old method: Place items in cart -> Arrive at checkout -> Take all the items out of the cart -> Scan all the items -> Put all items back cart -> Pay -> Go to car -> Take all items out of cart.
Scanner method: Scan item -> Place in cart -> Pay -> Go to car -> Take all items of out cart
You could even set up your bags in the cart so that when you pay everything's already bagged up.
Cutting out the repeated loading/unloading saves a decent amount of time and there's usually very little wait when you need to pay. Some stores in my country support using your phone as the barcode scanning device, it's very quick. I can imagine that at some point the phone could be used to handle the payment as well, at which point it'd be very close to the Amazon pick up and go model.