These companies want you to use the self service, so they can hire less people, which is exactly what has happened. I guess having more tills is useful for breakdowns and Christmas time when they hire temps, but I absolutely refuse to use self service, and in the case of some shops I've been in where NO tills were open, I made the on hand staff member scan everything through, and if they start trying to teach me how to use it I'd tell them not to bother.