For one thing, I hear blogs make you rich. Second, it's good discussion at parties. (though this goes without saying.) Third, I'm shooting for tenure, and this really impresses the committee. Fourth, programming blog posts are instant laughs, and a joke a day keeps the doctor away. Speaking of health, Benefit Number Five of programming and blogging is the sweet bulging biceps you get from coding, which in turn helps with Goal Six: aikido mastery. Seventh, a thorough understanding of programming helps you realize and comprehend the oneness of all things, so hopefully we can all learn together here.
Let's get the culture wars out of the way too: IDE's are the only goddamn reasonable tools to write code, the higher-level language the better, and git is the stupid content tracker. Oh, and well I'm gonna be rather biased in a Googley direction, although I'll try (try!) to keep that in check. Don't want to get all fanboy about it; it's only the best big software company on the planet.
(and in case you're wondering about perk number 8 of a programming blog: it's the chicks.)