There is no net effect in that everyone still has a seat, however that's not the point. An "A" BP passenger probably gave up a window seat and probably got stuck with an aisle seat that otherwise would have gone to a passenger with a "C" BP. The family should have gotten their early enough to pre-board.
seashoreCM said:There is no net inconvenience to others. If the family had been there earlier they would have gotten the window seat and whoever was in it would have sat elsewhere, exactly as if the flight attendant made a last minute request to move.