Although airline systems are designed to be full proof, they keep bringing on better fools. I'm sure KM is doing it for a reason, probably because some fool got on the wrong flight.
Recall a flight to BRS on an orange airplane a while ago. Before door closed frantic crews counting and recounting of passenger numbers, then an announcement "This is Squeezy flight 123 to Bristol ..., has anyone boarded this aircraft by mistake? Repeated in school girl French ... Silence, pause. Another announcement "We have an extra passenger on board, would anybody who is not flying to Bristol today please identify themselves to the crew?" Repeated in even worst French ... silence, pause.
Finally, ladies and Gentlemen, would you please have your boarding cards available for inspection, thank you. Repeated in, we'll you know, French ...
Finally a young man, in his late teens is escorted off the plane, protesting in very good French, that he thought he was flying to "Loo Ton".
And that's why many airlines check the boarding at the door.
True Story, and U2 crew did check our boarding cards for that flight.