Short list:

* I need to be productive/rested/ready when I arrive at a destination. When I do a day trip, nothing sucks worse than flying in a suit that gets wrinkled/spilled on/smelly from being jammed into a coach seat.

* I need to be productive IN flight - able to pull out my laptop and paperwork and work - very difficult in a coach seat without elbowing a fellow passenger.

* Because I am often daytripping, I sometimes run tight enough that I need to get in and out of the airport quickly (i.e. need to be first off the plane to get to a meeting or I get to the airport late enough that I'm near final boarding)

* In the same vein, sometimes I need to eat on the plane.

* Likewise, sometimes after a long day, its nice to have a drink (or three) too.

* And frankly, because I fly so freaking often (sometimes several of these day trips a week), it would get really old sitting in coach all the time. I've found that the first cabin (for the most part) is not as loud, tends to have less disruption (children, infrequent flyers, traffic in the aisles and over me in the rows), and causes me less "nerve damage" than being in the coach cabin.

* Oh, and because I can.