I have a fixed gear commuter with two sets of wheels. It's nice to have a backup pair for a quick swap in case you break a spoke or something.

Both clinchers with tubes, both aluminum, one is box section one is aero, one is a little wider, one will not take tires over 28mm. I keep 32mm on the wide ones but they don't fit under the fenders as well so I use them in the summer and the narrower ones in the Winter.