I wonder if there is a net job loss. For every cashier that's not hired, there's probably someone hired to watch the monitors. Is it really about diminishing payroll or is it about eliminating a bottleneck to the flow of merchandise and boosting convenience? I haven't explored deeply enough to know.
Self-service is the name of the game. Notice the steady increase in self-checkout in the big box stores and supermarkets. I'm old enough to remember lunch at the H&H Automat in NYC.
Here's the inevitable evolution of that trend:
http://www.pressherald.com/2017/10/17/no-lines-no-waiting-at-self-serve-portland-food-cart/