Reason #3: 10-32 fits M5 nuts. The pitch is very slightly different, so this only works for a short threaded length. They fit together nice and tight. It works great with the nuts for 20 mm aluminum T slot extrusions.
Anyone is entitled to look down their noses at this practice if they feel so inclined, but our team has years of experience doing it without having bolt loosening problems. I got the M5 & 10-32 idea from
these fine people, whose experience and expertise I trust very much.