Have you ever:
If you can answer "yes" to any one of these questions - you should be blogging.
If you can answer "yes" to more than one of these questions and you are not blogging, then shame on you! Start blogging today!
Don't think your opinion matters, or that you have anything worth saying? Stop fooling yourself. If you write code, you have opinions and preferences. If you have opinions and preferences, they are worth sharing. It's not possible to write code without opinions. Software development is not a mechanical process like building a house or a car - you can't sick a robot on a keyboard and write a functional piece of software.
The worst case scenario: If you post code examples on issues that you have solved, you will have a history of code you have written and issues you have solved. You'll be able to go back to this history and re-use existing knowledge, rather than having to think through the problem again.
The best case scenario: If you post your code examples, your thoughts on software development, your opinions and preferences; chances are that someone else in this wide world of ours has the same opinion or has had the same issues and will find the information you provide useful.
Why should you blog? Because you're a person with ideas worth listening to.
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Get started now. Register a domain name and buy some web hosting so you can have a blog that is accessible to the world. I use dasBlog and WebHost4Life. There are thousands of options out there - find the one that works for you.
Disclaimer The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.