Earlier quoted context omitted.
Along the same lines, imagine someone allergic to bees getting stung on the face causing their face to swell, so the system doesn't recognize them and they can't get into their apartment to grab their epipen. This system could literally kill a person
Heck, imagine something as mundane a haircut, a beard-shave, or a sunburn from a beach trip.
Also, face recognition technologies are better than described in the comments; you can take a photo of a random person from the street and successfully find their social network account with publicly available sites. Compared to this, recognising just several hundred faces looks like an easy task.