And as I said in my post above a closed check-lane is another enitity entirely. For some checkers there's a 30 minute process of counting the drawer, there's also other lines that that customer can go in. If a checker just helped people until no more came in their line they'd never leave on time because people would just keep coming.
This.
If one of our lanes isn't open, there's a reason. Either we don't have enough checkers, or somebody's on break or sick, or there's a technical problem. We don't shut down lanes just to spite people. We don't exactly have money to burn to hire 100 checkers for every day. We have to make do with what we have.
Fortunately, though, we have a whole separate department for counting down drawers. So our checkers don't have to do that. And we don't make people stay late, either (we are not allowed to do that, and neither is anyone else for that matter). If a checker is off, then we shut the lane down (unless there's a replacement handy). End of story.