When you have the time and the subject matter is something you are interested in (or even if you're not) you can learn a lot about something by just writing about it.
Part of it is finding the right way to say it. You can think you know something but then when you write it down it doesn't make sense so you are forced to re-evaluate your thoughts.
I heard a quote the other day: Everyone is wise until they speak.
I think it means everyone can look wise before they speak, but you get a better idea when they do speak.
But I think it could also be taked another way: you can feel sure of your ideas until you talk about them.
For example, you can be listening to two people talking and think you know where you stand, and think your ideas are correct and based on reason. But when you come to express your ideas, they don't sound as convincing, and you realise you hadn't examined those ideas as much as you thought you had.
So writing down you ideas is a good way of examining them, and thinking about them in more detail.
And, you could do that, or, some version of that in a blog or journal.
What have I done today?
I usually write what I have done today here, and I have found it useful for reviewing my day, looking at what has been beneficial and what hasn't, and thinking about what I will do tomorrow.
It took the form of a table and brief sentences describing what I had done. But I'm worried that Google sees it as a form of keyword stuffing so I'm going to stop doing it for a while.
Today, also, along those lines I've removed, the category list from the right hand side of the page (for all my journal entries). Which again was useful for finding articles in different categories but again could possibly be seen as keyword stuffing.
I'm going to re-submit my sitemap to Google today also to see what effect these changes might have on my rankings.