I confirm this doesn't do anything for your career, or at least not as much as just focusing that time on actual, paid work. I find that in my career my resume and experience that's on it as opposed to any side-projects or attempts at writing.
Yes, however on helping the career I think the writing is like a nice little detail on the resume, a way to make it standout a bit more, I also found that in a recent interview for a project an article I had just written on SVG was naturally relevant. As a general rule talking about little articles you've written isn't going to naturally happen in the interview because the interview process is focused on past work and horrible trick questions.
It has also been somewhat useful in projects where a concern with documentation has been expressed because the writing is a better example of my ability to document things than having worked on a lot of projects where you may be able to go see what we shipped but not be able to see anything of the documentation.
I think of the writing as the equivalent of a side project:
* it allows me to focus on something I want to learn
* it helps to make what I learn stick in my head
* it gives me a deadline and people who will send me emails to say how's it going with that
* it works as documentation for what I've learned
* it gives me a trivial amount of money for having taken the time to learn something. Basically the last article I wrote is paying for an annual Dropbox account, and a couple days worth of food for my family. It was way too much work for that to be worthwhile, but I did learn some things that will help with later stuff.
