Germany's discounters (ie, nearly all grocery stores) have long been hyper-efficient about checkouts. There is exactly one lane open until the line gets too long, then they open another. When the number of customers subsides, the second lane closes and the employee goes back to other tasks.

Only in recent years have self-checkouts started appearing in any significant number, and the formula hasn't changed. I guess theoretically stores might be able to cut back on employees, but it would be literally one or two people at most.