Purge valves in masks

I haven't notice this topic covered, so apologies if I am rehashing an
old subject.

Three years ago, when my daughter got her OWC, we selected a mask with a
purge. While she learned to clear in her class, it has never been
necessary on any dives. The mask works very well. So well, in fact, that
I opted to buy one for myself when I replaced my old mask last year.
Boy, is it great. I've used masks to snorkel and dive for over thirty
years. All of them leak at some time or another, whether due to poor
fit, hair not removed from the skirt, whatever. My new mask, with purge,
stays bone dry all the time. This also seems to keep the fog down,
although I'm not sure that it is a cause/effect relationship.

Some might think that it is one more item that is unnecessary and it
adds another potential failure point, but the purge is a pretty simple
little device, and as long as it is kept clean, it should do its job
reliably. For my money, I'll probably always use a purge mask from now
on. But I haven't noticed too many other divers using them. Why not? Am
I missing something (besides the need to clear)?

Bart F.