It wasn't about the cashier, it was about the line.

Before self checkout, the wal mart near me would on a typical day have 3 or 4 cashiers working. At the height of their adoption, they had 28 self checkouts typically up.

But now, they have 2-3 self checkouts open and a big line, while you can generally find one of the handful of cashiers with no one waiting. It baffles me that people would wait to self-checkout when there's a cashier open with no line, unless people have just that much social anxiety (a wal mart seems a tricky proposition) or else people are liking their chances for skipping scan of an item here or there.