I never understood the appeal of having to do that "work" and still pay the same price. To me it feels like going to a restaurant where you have to be the waiter yourself. Is that really that convenient?
Yes it's pretty convenient, no need to take items out onto the checkout counter just to put them back into my shopping cart.
The Sam's Club version, scanning barcodes while putting things into your cart, means you get to skip the checkout line completely. That's an easy 10+ minutes saved if the store is busy.