Personally, I think blog is like a blackboard! Teachers can post things such as class syllabus or class plan on the blog just like they write things on the blackboard. The only difference is that information on blackboard has to be erased after a class, but the information on blog can exist for as long as the blog exists. In this case, it makes teaching more efficient.
Firstly, the student can frequently review teacher's post about class on the blog which saves teacher's time in explaining many things. Using the blog, student may get very clear about questions like what the assignment is for this week, when it is due and what they need to read before the next class. Such infromation will always be available on the blog. In this case, nobody can say they don't know what the assignment is.
Secondly, teachers can offer links to many learning resources for students on their blog. It's convenient for students to check those website links to get useful infromation.
In addtion, not only teacher can post things on blog, but also students can feel free to post their comments and ideas about the study topics. Many students like this kind of interactive learning and would like to read and share good comments and ideas from their peers. Also teacher can get student's feedback from the student's posts. It's a better way to know student's learning progress by reading these posts than reading the assignments only.