And if your phone gets lost or stolen in the middle of your international journey...
Or just runs out of batteries and you don't have a charging cable. Maybe you could ask a stranger for help, but you're in a country where most people don't speak your language. Or maybe people do speak your language, but you have a phone with a charging port that isn't standard in the country you're in. Also, you're about to miss your flight. I think we can all agree that edge cases will always exist. The question is…
I’m a Global Entry member. I am already in all the databases ever, because I’m a doctor, so I just said f it and signed up. The facial recognition systems used by the US government- - if they get a well-posed picture of you (presumably with a lot of 3D detail) - are absolutely fantastic. I don’t even pull my passport out when returning to the US. I get a picture taken at a kiosk, I walk up to the line on the floor, and the agent says “you’re good, Devilbunny”. That’s it.