This sounds like your homework. Could you elaborate a little more and give us some context? If you gave us your opinion as well, that would be more helpful instead of just expecting us to hand over answers.

Because the student needs to practise speaking. Advice from the teacher can be given in writing any time before or after the lesson, but during the lesson is the only opportunity for the student to talk. If the student wants to practise listening, then they can use TV shows instead. So, a teacher talking during the lesson is undesirable.

Hello, could you explain a little more what you mean, the context? thanks :)