The purpose for the vent, as I understand it, is to vent CO2. So no venting would mean, uh, no venting. Get that mesh wet, put your hand over the end of the mask mini-tube, blow out with all your might, and you will find that no air can escape. I personally have not found that to be the case with any other mask I have had the privilege of using. Other masks I have used not only still allow CO2/air to escape but actually allow water droplets to escape during mask use. So it isn't a matter of airflow into and out of the lungs, or a matter of pressure, but a matter, I believe, of buildup of CO2 that is at issue. For me, at least. And that's just because I choose not to use the climate-control hose because I prefer a lighter hose on nasal masks. I doubt this would be an issue for anyone using the climate-control hose to prevent rain-out. I love that word "issue"; it has such a nice mental/emotional ring to it.
But, hey, I'm just some crazy guy on the Internet punching holes in medical equipment willy-nilly. That's why they won't allow me inside the space station anymore. So no need to take my crazy ideas seriously. I don't even listen to me half the time.
