When traveling (not currently) I started carrying and using my Global Entry card after managing to lose my license between the curb and security a couple years ago. This way I keep my license safe in my wallet and just get a card out at a time when I'm usually tired and juggling stuff that doesn't really matter much if I lose and have a backup in my bag.

In what case would you use the Global Entry ID card over a passport?

EDIT: Thanks for the replies everyone, TIL! Will have to see if TSA can use my GE ID card to lookup my boarding pass (like they can do with a driver's license, passport, or DoD CAC) next time I fly.