I certainly think about what I'm going to wear when flying. I want it to be comfortable - my feet & legs have, on occasion, really swollen while flying. One time, I couldn't put my shoes back on when the plane finally landed.
I also want to make sure that I wear my bulkiest clothes/shoes on the plane to save space in my suitcase.
And finally, I want the airplane clothes to fit in with the remainder of my clothing.
I can pack for 3 weeks in a carry-on suitcase & still have room for souvenirs, but it means that EVERY SINGLE ITEM is chosen with thought.