I don't blog often, but I do like to write down my thoughts or things I have learned, and share them with others.
Frank Viola, on a podcast from a few months back, talked about reasons to blog. He hit the nail on the head as far as why I blog. If someone looks me up on the internet, they will come across my blog, and it will explain who I am and what my passions are.
You can listen to that podcast here: http://ptmin.podbean.com/2013/03/03/how-to-start-a-blog-why-every-christian-should-have-one/