I hate to say this, but I disagree with the majority of the group here. I take my mask off for just about everything. I have a hockey style mask. I was taught, and even college coaches and players that I work with told me, to take the mask off for pop ups and if possible for bunts too (but that has to be quick and no time can be wasted for that!!). I took it off if there's a chance of a play at home too. I know teeth can get knocked out, but hey, it's a chance you take. I like it better without the mask. I have great view of everything without feeling like a bobblehead. Girls try to run into you, but you learn to try to prevent some of that and still get the out.
I remembered this thread from a while back ago. I have a dd that catches. She is doing good, she just needs to be faster on her feet. However I had a parent of mine come to me and tell me my dd would do better if she would throw the mask off. She still harasses me to train my dd to take the mask off. Why wont she just go away!!!
but more importantly it is protection from impact from another player.