Used it a lot at my old work. It was a very small company (<10 employees) but had people scattered over a few locations.
The way we used it mainly was to replace group emails as well as eliminating the need for stuff like post it note lying around (minimalist, paperless office). It worked pretty well- it was possible to ‘tag’ people in post so that you were sure they would be notified, or you could just scroll through every department (at least the ones you were allowed to see) to see what stage other projects were at etc.
Come to think of it I might suggest it at my new place!