Not to long ago, Sacramento airport had a computer glitch and the only people allowed to board were those with paper boarding passes. I'm a "no paper" guy and if I can save it to my Apple wallet I do. It was great when the Safeway pharmacy sent us links to our VAX records with QR codes. I put my boarding pass in my Apple wallet also, just in case. I'm not a big fan of Hilton's digital key however, it seems to not work more often that it does work. But the online check in is pretty sweet. All that being said, my paper copies aren't to far away if needed.