Making sure that all passengers have a valid boarding pass when they board the aircraft actually helps to makes sure that "no people who haven't been screened are able to board a flight"
Presumably using their cloak of invisibility to get past security and the man at the end of the air bridge. Orders are orders but I'm afraid people don't really believe you when you say it is helping things more than it hinders progress alas. It's no more believeable than the need for security staff to steal water from people. Theatre, theatre, theatre.