https://www.vox.com/recode/2019/5/1/18511575/productivity-slack-google-microsoft-facebook
Much like the ubiquitous open-floor plan, this type of software is meant to get different parts of a company working together, to break down hierarchies, to spark chance interactions and innovations.
It would be physically impossible for any employee at a big company to read all their Slack messages and channels “By lowering the barrier to initiate communication, the hidden side effect is that Slack has the quiet capacity to exponentially increase communication overhead. Resulting in much more voluminous, lower quality communication.” In other words, talk is cheap and we’re spending like crazy.