Disadvantages of a "If I didn't see it,It didn't happen' policy?

I don't want to ramble too much,but i just want to give a few details.My orchestra teacher has an "If i didn't see it,it didn't happen" policy in his class.In one way this could be cool,if you're just like horse playing and don't want any mix-ups.But in a few instances this has been bad.For example one of my friends got locked in a bass locker,and he almost got stuck in there!Another occasion is when people doing really stupid childish stuff,like climbing on chairs and throwing bows.Keep in mind this in an 8th grade class.I don't want to ramble anymore than i already have,so i'll just ask the question.What are the advantages and disadvantages of a "if i didn't see it,it didn't happen policy?