I can't pretend to have familiarity with the subject taught in this guy's class, but as someone who teaches a subject that requires multi-step derivations, it c

I can't pretend to have familiarity with the subject taught in this guy's class, but as someone who teaches a subject that requires multi-step derivations, it can be really devastating to have interruptions. I do not have such a policy in my courses, but I can understand why someone might want this. The autonomy of the instructor and his/her ability to set policies that will ensure the common good in their class is an important cornerstone of academic freedom. People who would complain about this probably don't understand this principle.