The company I work for uses this for internal communication. Workplace is basically the same Facebook and Messenger, but tweaked for a private group of people.
The problem is that, because this is basically the same Facebook, it is designed to keep you "engaged". It uses all kinds of patterns to keep you addicted to your timeline and search for attention. Rather keeping you informed with the important topics, it distracts you with a lot of irrelevant stuff. The algorithm will always show you something that keeps you scrolling. Huge time waste.
The motto of this software is "Bring your company together". And it works exactly as Facebook's motto, "Bring the world closer together", in the sense that it does exactly the opposite. The software has all sorts of mechanisms to generate controversy. Because controversy is what ultimately drives more engagement. Reactions, memes, notifications. It makes you fight with your colleagues about silly things, and it makes it really easy to derail any sort of constructive conversation.
Imagine having to try a technical conversation in this platform and then people are allowed to "react" with an angry face or a silly animated GIF. No argumentation required. And those reactions will bring more reactions. And in those rare cases when some meaningful discussion actually happens, then the thread is quickly buried by the constant stream of new things.
If your company is considering this, avoid it like the plague.