In my experience, it’s used as a recruiting tool. High quality talent is usually attracted to orgs with a transparent culture, and well-written blog posts show that the culture is healthy to external talent.
To be fair, if the culture is disfunctional I'm not sure that anybody is blogging about it, and I doubt they pick dumb mistakes and bugs to blog about. "After three days of troubleshooting DNS, and a two hour blamestorming session, we checked the logs and there was a leading space. Don't be like us, kids."
If a company does not allow its engineers to participate on mailing lists and in the open source processes... sigh. There are an awful lot of stilled voices out there.