> It saves you a bunch of money and time and also trouble and worry if you can move from checking bags to not checking bags

This has been my experience, too. Some airports have a half-assed process where it's partially self-service and partially done by a human. In Denver, they have booths outside to check bags. You scan the QR code, pay in the app, and it prints your tag at that booth for the worker to take. Convenient right? Wrong.

I'm second in line, so I scan and do the whole process, then the worker leaves to help a disabled woman. No problem I thought: I'll just go to another booth to have it re-printed. Nope, apparently once you print the tag, employees can't do anything about it and you're forced to buy another checked bag or hope that the original worker comes back (I'm not taking that chance if I have a flight to catch)