In some parts of the world, you don’t need a boarding pass to clear security and in some of them you don’t even need to be actually travelling (especially if you are assisting others in boarding or check in).
AC issues gate passes for those people.
Keeps the riff-raff out.
Too bad those annoying non-flying, credit card peddlers have no problem getting past security though. I go out of my way not even to make eye contact with them.