I would imagine it's great for detecting who is goofing off when they should be working. We've had it at our office for 2 years now and, as near as I can tell, only the people who want to look like they're drinking the corporate kool aid have accounts.
People write amazingly crazy things in a public forum. One guy wrote and posted a 40 page manifesto about why we should replace PCs with 3270 terminals. (Not kidding)
A support guy posted ASCII dick pic art in the all company forum.
We had some Bernie Sanders v. Ron Paul showdowns.
Overall, it has been really good. It's the go-to place for general HR questions. It's a great place to solicit testers and feedback. Definitely a net positive.
It's also good to spot talent. We use this stuff for outreach and the "consulted", "informed" parts of RACI projects. Works well.