There are really three reasons why I blog.

1. I like writing down various events or thoughts in my life.   I get a feeling of closure once I have documented something that I wish to remember, would like to refer back to, or be able to share with others and link to. Basically, I do the blog for myself.
2. I like to give back to the development community.  When I've researched extensively a  problem I'm having coding, and I find the solution,  I publish it here in hopes that I might save someone with a similar problem some time.  For example, THIS post is #1 today, in Google search for the phrase "xcode breakpoint" which probably means that Google has decided it is very relevant and people are benefiting from it.
3. I like to give back to others.  Same as #2 but more on a personal than a professional level. THIS post is #1 in google as well for the phrase "Why music is important in our culture".  It is the post with the most comments.  People don't generally leave me a comment unless they REALLY got something out of a post.

I spend a lot of time searching the net as I'm sure many of you do.  Most of the content I read are not news site or commercial sites, no, most of them are personal sites and blogs.   I try to give back to that community since I'm an avid consumer of it.