You can’t read any marketing material without hearing about social media – Twitter, Facebook, LinkedIN, Google Buzz, tec. — but blogging is also a social platform. Twitter is defined as a micro-blogging service. Instead of a whole paragraph or a whole page, it is a 140 character blog post to the Twitter service. Who says you can’t blog?
A bunch of reasons including to demonstrate your subject matter expertise; for publicity (PR); to become a Trusted Advisor; for reputation; or to just be heard.
In general, you blog for marketing.
A side effect of blogging (and other social networking) is SEO (search engine optimization) – or at the very least, search engine results. If you create enough organic, genuine content around your subject or topic (or keyword), the search engines will ikely find it (eventually). The more content and the more frequent you create content, the better your search results. So blog often.