I would assume it's just the pilots preference, weather, etc... Just like if it's a nice day out (and i'm not on the freeway), I prefer having my windows down over using the AC
. Plus it's probably nice to open the canopy after having it closed and being all cramped and confined in there after a mission. First thing I do after I land my Cessna (even before i'm off the rwy) is open the windows just to throw my arm out and get some fresh air.
Just my two cents