A Picture’s Worth says:
You probably don’t add images to your portfolio everyday. You probably don’t shoot a wedding every day. And you probably don’t add stock images to your archive every day. In that respect, the “main” part of a photographer website can be fairly static.
Blogs, on the other hand, are a great way to talk about the photos you take, the projects you’re working on, the photo workshops you’re attending (or running), etc. I fret when people conceive of blogs as an online journal because I’ve always believed that the real benefit of a blog is as an SEO machine.