My goal was to introduce a culture of internal blogging at the company. I didn't really succeed on that front - I used my blog a bunch and a few people made a post or two - but I like to hope that if I'd kept at it for longer (I left the company) it would have started to catch on.
The reason I like internal blogs is that they release you from a lot of the pressure of writing more formal documentation. If there's a technique that I think is a good idea but that has not been established as an agreed best practice, writing it up in official documentation doesn't feel like the right thing to do. Writing it up on a personal internal blog as "as-of date X my opinion is that we should do Y" is always OK.
Likewise: writing documentation that later goes out of date can cause harm. Writing a blog entry that says "as of February 2020 this particular system worked in this particular way" seems much safer to me.