Also, the workers who load your cart at Costco seem to be trained to pack it for easier/faster scanability by the exit-check people. Plus IIRC the receipts split anything they leave on the bottom rack of the cart into a separate section. Neither of those things happen with self-checkout, I suppose (I've not used the self-checkout yet, because the regular checkout is so fast at Costco and they're well-staffed enough that I haven't wanted to)