Number 10 screws seem to be the transition point between using course threads (larger sizes) and fine threads (smaller sizes).
During my entire career spanning various industries including aerospace, semiconductor equipment and other hi-tech fields the standard practice was 10-32. I never asked why, it just was. I believe part of the reason is that this was the fastener sizes companies stocked.
Recently I see an uptick of 10-24 usage. Curious.
What is your experience? What industries have you see one or the other or both?