[henrikschroder]

Another thing is that if everyone at a location has to be serviced by a person, then everyone currently not being served have to wait in line for their turn. They're not doing shadow work, but they're equally improductive.

Airport check-in machines are a fantastic thing because it speeds up the process. The airport can have ten times as many machines as desks, and that means your check-in will be about ten times faster. That's a lot of time saved that you can use for something else.

And you can still have service personnel and machines at the same time. I can check-in at the desk or through a machine. I can withdraw money by going inside the bank, or use the ATM outside. I can do the self-checkout in a store, or have it done by a cashier, and so on.