Advantages: You can embed pictures, videos and links into the message content, which is great for posting your class assignments. It's easy to reply to a post and see all of the other replies to that post at once, which is a plus for teachers and students. And it can be set to private, so that only group/class members can post comments.
Disadvantages: Only the blog administrator can post an original comment, so it can be difficult to start a new discussion thread.
It seems like a blog is better suited for a teacher than a student, since one person is making original posts and controlling blog membership. A blog would be very useful for providing assignments, making announcements or posting lectures.