Pretty sure that one human employee could scan groceries 4 times faster than people doing it themselves, so those self-check registers are saving them... absolutely nothing.
No, over the many months we customers have gotten better at self checkout and have learned not to trigger the events that will require that employee override. And they now make the bags generally available, we no longer have to interrupt the employee to get bags.
although I'm not sure whether it is due to intentional or accidental failure to scan items
Failure to scan triggers one of those employee overrides. The system is quite sensitive. If you try to scan things two handed, sequence items one at a time, a little body rotation can get the second unscanned item in the other hand too "near" the bagging area and trigger an override. There are RFID and numerous cameras tracking each item. You can see it all as the employee clears the false alarm.
When I hear a beep, I assume the item scans. Turn out I can't tell the beep from the register I'm at from the beep of any of the adjacent registers...
And that will get you one of those employee alerts.
Good luck when someone leaves something behind accidentally in the bagging area. That's something the software can't handle. Its not on your scanned list but it can't be moved off to the side out of your way without an employee alert.
At first with the self checkout you move glacially slow and it works. Then as you get more familiar you try to work faster and trigger all sorts of alerts, sometimes multiple in one checkout. Over the months you get the movements and pacing down well enough to avoid triggering alerts. And you can now go get a bag if you need one yourself. All without employee intervention. Once the customers get "trained" for checkout the system may very well save money. I wonder if they are counting on us customers gaining such proficiency?