We've adopted to doing practice courses on my university, and one course decided to have a lot of assignments handed out.
Once I, as a student, handed it in, and the teacher graded it and assigned a comment, I had no way of replying there, only in Chat. So if a teacher comments there to ask something that helps him to grade the assignment, I have no way to answer there, and it can lead to confusion, if you have to refer to chat.
