Beyond the great points that have already been mentioned, greater likelihood of overhead storage space really helps. Especially when I'm only traveling with carry-on luggage so that I don't have to deal with baggage claim and can be off the plane and to my hotel/home/office right away.

Granted, I can board early with AA status. But sometimes my connection gets me to the gate after boarding has already begun (especially since, with carry-on only flights, I'll book myself shorter layover times because I'm not worried about the luggage not making it to the next flight in time) or I slither out of the Admirals Club a few minutes too late.

Hate not being able to get overhead bin space, hate having to stow my carry-on further back than I am seating (last person off the plane!).