A blog post every day for three months means I'm now just shy of having written 100 posts! I can't believe that I've made it three months without skipping a day, even though we've moved house.
These blog posts have helped me in unexpected ways. Sometimes the act of writing things down helps me to think through a problem. Other times it's just helpful to have documented something when I want to look at it again later. It's also helped me to be more clear and less ambiguous when having to communicate things to others.
None of these things require me to write them in public on a blog, but having it public somehow helps me to be a bit more accountable and to keep the habit going.