Being published on the internet for all to see is a great motivator. Especially with regards to accuracy.
A blog is Attractive: No more scrappy notebooks
A blog is a valuable resource for weaker students because they can copy the stronger students work.
It is easy to edit a misteke out of a post.
Individual responsibility: The student owns the blog
Pastoral care: Like a diary, you find out about their personal lives and are able to step in if appropriate.
Rapport building: This was an unexpected side effect. I find that my students discuss food and end up going out to dinner together. This happens every term. Weird.
Another unexpected side effect: Blogs provide an equal voice for quieter students
Less marking: There is not the expectation that the teacher will go through the writing and mark every mistake. When you do point out a mistake they rush to correct it because everyone can see it. Students feel validated when their classmates leave comments on their work, reducing the need for teacher input.
Cut and paste error feedback: In 5 minutes you can cut and paste a selection of student sentences into Microsoft Word and have an instant error feed back lesson.