1. Blogging is a very good way to help sorting out own ideas and shape thoughts on a particular topic. Unless you write it down and try to express your idea coherently, thoughts are just bouncing inside your head without proper actionable output. I notices from my own experience that ideas form and progress much better when I write them down.
2. Blogging is helpful as a form of journalling about particular topic—to return to later. Sometimes I read my old posts to refresh my memory and often get surprised that it was written by me—after some time I forget what was the logic that led me to a particular idea or descision and old posts look like written by somebody else.
3. Blogging helps to discipline oneself. Writing and editing takes time and effort. Only regular stable blogging attracts any audience at all. Not that it's important, but it's good feeling when somebody finds what you wrote helpful. Many just want to get audience without understanding what it really takes. It's not that easy. So, as a byproduct of the first two points, one learns what it takes to produce good content with a regular cadence.
It takes effort to carefully write, edit, and rewrite. But it really helps with our own thought process, improve ability to shape ideas, helps save sorted out ideas for later, and disciplines ourselves.
So, I'd say blogging is a pure self-improvement exercise—fitness for the mind.