Its not just about SEO
Many "tip" sites will insist that blogging is important for SEO (Search Engine Optimisation) and whilst this is mostly true, there is a more important aspect. I believe that the ongoing conversation that you are having with your audience is vital to your success. This enables you to widen your audience and help people understand the source of your inspiration and also the path that you have taken and where you are moving towards. As you document overtime, it enables people to see your origins at whatever point they find your work. This enables people to understand and get taken deeper into your work.
Personally I love the immediacy of contact and feedback. You are not waiting for your first exhibition or for a gallery to pick you up, to start engaging with you and your work.
Where you are a more established artist, it enables you to publicise and feature new works.