It's unavoidable. At some point — if not on a regular basis — as a developer, you will need to produce some type of content in written form to share with your team or others. Since clear and concise technical writing takes practice, it makes sense that you should make a proactive effort to practice your writing. Writing a blog is a perfect (and an easy, low- or no-cost) opportunity to get some practice.
There are plenty more reasons, however, why blogging is beneficial and useful for all developers. In no particular order, here's why you should be blogging: