I believe that writing is an essential skill. Like writing code, pure writing is a skill to be worked on continuously. Clear writing indicates clear thinking.
One area that writing or blogging will help immensely is in an interview. Interview questions are fairly predictable, and the ability to respond naturally and clearly is a major advantage.
Here are some interview questions to not just think about, but to write about:
There are classic questions in our industry, and you should have an opinion on each of them. If you've blogged about the issues, you've already struggled with how to structure the response, sifting the important information from the irrelevant, highlighting the critical points. In an interview setting, this is incredibly beneficial. Your responses will be polished and clear, and you will leave a great impression.
It's hard to predict specific technical questions or code challenges, but those tend to be later on in the interview process. The opening questions are more conversational, with the interviewer assessing your overall communication skills, technical inclinations and abilities. If you display clear thinking and well thought-out responses, you'll make a good impression and set yourself up to succeed later on when things get more technical.
So if you are in the job market, polish your Github profile, fix up that résumé, but make sure you've spent time writing about the big issues in our industry, and in your technologies of choice. It will be worth the effort.