Students can submit a comment on an assignment through Grades, but not through the assignment itself. Students are able to do so through Canvas Student, so it would be nice for the feature to be available on the web in the same manner.
Canvas Student users can add a comment to an assignment before or without an actual submission. This is awesome for students who ask questions regarding coursework. Students are asking about assignments in context, and as an instructor, it's helpful! I don't have to try to guess which assignment they are referring to as they type a message that goes into Conversations Inbox. I think this (inquiring about an assignment through Assignment vs Inbox) is routine for my students as they all have iPads, however. I also enjoy the feature for when there are multiple submission formats permitted. The student or I can leave memos of face-to-face conversations as well.
Until a few months ago, I did assume that this mobile format was duplicated in the browser. I was wrong, and I was really surprised!
In classes where students have access to desktops, this feature is only available through Grades. While helpful, this route is not intuitive. (How do I view assignment comments from my instructor?)
I'd like to see the comment feature be available on the assignment page itself. That way, students would not have to return to their mobile devices to leave a comment if they are unable or are not ready to submit.