Yeah, the adjustment period is kind of intense. I got barely any sleep for three weeks and then my body was like "ok I guess this is what we're doing now"
It basically gives more surface area and a smaller hole just for the mouth and nose, making it so it gets a better seal and doesn't have to deal with the facial hair.
I had to adjust both the 'fit' and to getting used to it, but it didn't take as long as elalmadelmar thankfully. But once you start seeing the benefits it's like night/day.