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.
Not sure I qualify as 'high quality talent'....but I have rarely read an engineering blog where I didn't think, "It would be fun to work there."
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."
Actually, while I like a well written corporate engineering blog, it is knowing that the individual voices within an org are allowed to blog, and for that matter, post emails to mailing lists, without oversight, that I find attractive.
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.
