Grocery stores are full of inefficiencies, but the operators do realize it and try to balance performance with operational expenses. It costs a lot of overhead to have all-lanes-open, and the non-food-value added cost gets added to the price of food items. In a way to improve checkout efficiency, lots of stores employ checkout conveyor belts that allow customers to load the carefully selected items to be checked-out while the attendant is moving items along at the front. This enables the “workload” to be buffered for the checkout attendant (“the processor”). The FIFO buffer approach ensures that the workload is ready for operation when the cashier is able to pull it. If not for the conveyor belt, checkout throughput would be severely limited by the rate at which the customer can directly transfer items up to 2-3 at a time from cart/basket to cashier. See system diagram:

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