Some of the things that search engines like Google factor in for the relevance of a web site is content and link popularity. Since content on a web site seldom changes, it may become stale. So having a blog incorporated to your site can help keep content fresh and give you higher ranking. Also, since Google gives more weight to in-context links, having a blog gives you ample leisure to link to your webpages from the content of your blog postings. Social bookmarking allows readers to bookmark your post, disseminating your links and giving you added exposure to other readers who may click through to your web site. If you post an article on your blog and it gets syndicated, with your signature and web address you can generate up to thousands of inbound links to your website boosting drastically your link popularity, thereby lifting your ranking. High ranking always translate into more traffic. Of course people who read your blog are more likely to visit your website if content is relevant, and may tell a friend.