If you are wearing a well-fitting N95 mask, it should be providing a good seal on exhalation and inhalation.  That is why masking works to prevent spread and protect others.  And while one-way masking is good protection, science has shown us that universal masking is even better. 

Also, it actually does matter what we do at dances, but it is because we are part of society as a whole.  If we have covid spread at a dance, every one who was in that hall was exposed, and they all have to go out in the world and encounter other people.  And if they are not wearing masks when they do that, then there is that potential spread to others, and so on.

Required masking at dances shuts off all of those vectors.