I share their preference. The cashier saves me no real amount of work. The difference between putting my groceries on a conveyor belt and having a cashier scan them, and me myself dragging my groceries past a scanner, is somewhere between minimal and non-existent. The amount of work I perform is functionally the same. The biggest difference is in the amount of time I spend, where the win clearly goes to the self-checkout, since then I can bag my groceries at the same time as I scan them, and there's more self-checkouts available than normal ones, meaning I spend less time queuing if I use those.