In the case of groceries wouldn't you only be as fast as the slowest line? Your comment only applies if all lines are equal, which they almost never are. So yo

In the case of groceries wouldn't you only be as fast as the slowest line? Your comment only applies if all lines are equal, which they almost never are. So you can't assume perfect load balancing under this circumstance. I think the best store queueing system is to have one main queue that distributes customers to the first available cashier. People with larger loads take longer, but this has little effect on the main queue.