First, I use the blog as a sort of lab notebook to record notes about and experiences with my personal projects, which I reference often. Second, I post ideas I want to share so that I don't have to repeat them over and over in online discussions.
As a bonus, the occasional post gets shared on Hacker News and generates a lot of interest.
Also, I hope that little snippets I've posted to solve particular problems, eg how to post a toot directly from Java which I couldn't find elsewhere and know wouldn't be hard because it's one line in curl, will help others, eg:
https://www.earth.org.uk/note-on-site-technicals-68.html#202...
Rgds
Damon