I jumped my old boy over some pretty dang large oxers unbooted.
I only ever booted him for competition. Partly for looks, yes, but mostly for protection because we took some INSANELY tight lines and he was at a higher risk of interfering with himself than he would have been just training at home.
As far as I'm concerned if you ONLY jump with boots on, and you leave your boots behind when you go to a show, you're in trouble! But if you never jump with boots on at home, and you forget them for a show, you're okay.