Answer:
I believe that mirrors are necessary because, say you're learning ballet, the teacher might show you something and you might need to look into the mirror to see if you're doing it right. They might distract some people, but I think that they help more than they distract. The reason I say this is because I have past experience of taking ballet, so I'm used to using the mirrors. THat is why I think mirrors are necessary.
Explanation:
Hope this helps! :3