I don't even think it's about going faster. In my experience, a traditional checkout staff is much faster than the self-check out. First of all, it's fantastically batched and pipelined. While the person in front of me is being checked out, I load all of my groceries onto the conveyer. Then, when it's my turn, the clerk does one motion over and over very quickly, and puts it on another conveyer that whisks it out of the way. When there's dedicated bagging staff, it's even more parallel.

Contrast that with self-checkout: There is no conveyer. You have to reach into your cart, grab one item, run it across the scanner, and place that item in a bag, then reach back over into the cart, grab one item, and so on. No pipelining at all.

I go the traditional staffed checkout route for the speed.