I’m building a number of apps. The need is simple. Let me explain.
Having a MAC Address, because it’s unique per device, you (programmer) can auto-save certain settings WITHOUT needing someone to register.
And by auto-save, I mean you could store settings to something like an AirTable without needing the user to register. Just save a record with the MAC Address and settings 1, 2, 3, 4, 5, etc.
If user deletes app and reinstalls it. You (programmer) could look up device ID in AirTable and prompt user as to whether they would like to restore settings. I would never recommend doing this with any kind of sensitive data, but it would be good for other data.
People get tired of the registration process for everything just to use an app. You could also do stuff like “remember” preferences, and if a user uses multiple apps you design, those preferences would automatically get used in your other apps. Stuff like that.