Maybe not so much a blog, but I believe a developer should maintain their own website, whether that includes a blog or not.

It lets you define yourself and organise your own projects. And (I believe) most importantly, you learn how to maintain a project over many years, which informs you of the most important decisions that need to be made at the start of a new project.

Does this help you get work? Who knows?

In my case, I have been approached by people who saw my website after reading an on-topic comment on this one :)