the answers will probably be as different as the people giving them. I do not read blogs (if I do at all) for information but for the writers response to it.
I am writing a blog about twice a month, and in it I endeavor to give my opinion on subjects. The subjects are usually fitness related but I have also veered into observations of everyday life and even politics. I want to give the reader (if such person actually exists) a more comprehensive view of me as a person. A person looking at my profile and contemplating contacting me will have a good picture of myself which enables him or her to assess compatibility.
I do not write for information as the main object. There are better web sites on any subject that I can think of. But I may write about anecdotal observations as they relate to specific situations. As am example, I have observed in one client with MS good responses to a certain approach and wrote that much in a blog.
By the same token, I am quite aware that such public exposure can have its risk, and I keep that in mind when I write because it is equally possible to make a public fool of oneself.