I'm one of the old people. I WAS a speed runner. About 40 years ago, I got a union job as a cashier. The customer put their items on the belt, the cashier scanned the items, and the bagger sorted the items and put them in paper or plastic bags. Cashiers were required to memorize the produce codes and process at MINIMUM 30 items per minute. The timer ran from the moment you unlocked your register to the moment you relocked it or opened the drawer. You would leave your register locked while the customer started putting things on the belt. You greet them and make a mental note of what sort of items are where while the belt brings the load to you. Once the belt is at least half full, you'd unlock the register and start grabbing and scanning items in a fluid motion that passed them over the scanner and on towards the bagger -- sorting as best you could as you went. As soon as you were done, you'd hit 'total' and lock the register until the customer was ready to pay. You'd help the bagger and chat while this happened. Then the customer would hand over cash or check (they were just starting to do credit and debit in grocercy stores so those weren't common), so you'd unlock the register, take their payment, open the register and get change. Your best speeds were always going to be for express checkout (10 items or less), but there is a cruel loop in that because managers schedule fast people for express, but you won't be as fast unless you get scheduled there.

As I recall, we didn't get to see our items-per-minute until the end of the day -- not per-transaction, but it was still fun to see who had the best scores.

As a customer, I NEVER use self-checkout because: 1) I'm not working if you aren't paying me, and 2) every time I've tried to use self-checkout, the machines could never, ever keep up with me. Sometimes the issue was the bagging area was trying to weigh things, sometimes the scanners themselves were bad/slow, and sometimes ... I don't know, the dang machines are just barely working? Anyway, it is never worth it for me. Additionally, I find it better to do my own bagging than to allow anyone else to do it.

Side note: The typical bagger can not bag as fast as a cashier can scan because they have to wait for: cans on the bottom/bread on the top, frozen in one bag/lettuce no where near frozen, detergents and chemicals by themselves/pet foods also by themselves.