Blogging also allows for a form of "social networking."
This can be as simple as linking another blog. In many cases, doing so will create a track back link to the linking entry. This provides a blogger with an opportunity to gain some additional traffic.
But there are a variety of free Web 2.0 services out there that can enhance the chances of other people linking to your site and sharing what they have found with others. Digg.com, Del.icio.us, and Technorati.com are a few of many tools that people use to store and share content. In all these ways a blog increases exposure for a website.