I've heard the same thing, and I'm not sure if it has any truth to it.
I shaved pre-T because I had something of a mustache happening (well, darker vellus hairs, anyway) and a few stray terminal/androgenic hairs on my jawline. It certainly made me feel better shaving, even if you had to be within a foot of me (and within my personal bubble) to see the difference.
If you're considering it, I can't see the harm in trying it out.