You board first as first class, because you have time to put your suit jacket up, and get your first free beverage, before they have to confiscate the cups for

You board first as first class, because you have time to put your suit jacket up, and get your first free beverage, before they have to confiscate the cups for takeoff. If you boarded last, you'd get no pre-takeoff beverage to sooth your nerves. At some airports, they board the larger jets through multiple doors - First/Business gets their own, and everybody else crams into the other one. I've also been asked to wait to board while the first class gets situated and has their pre-flight drink. (I've also had that pre-flight drink, and it's pretty nice!).