Blogging makes you notice
You look at your writing and start to notice patterns in them.
For example, I noticed that my learning blog posts are sometimes not as deep and detailed as I would like. I noticed there are some questions that I could ask when learning about a project that could help me gain a deeper, more useful insight into the project.
Also, published blog posts work much better than private notes or tweets, for reminding you of a personal insight or learning you’ve had.