As much as I want to argue that everything should be backed up, I realize that consumption devices would be a waste of time to backup if you are careful not to create any new data on them.
I have a couple of Linux Mint Debian Edition instances that I intentionally do not back up. I have Android devices (including Kindles) that I do not back up.
As long as the person is rigid in not creating data on the ‘disposable’ systems, I agree with you.