Speaking solely from personal experience, I find that Async helps keep everyone on the same page. Rather than needing to scroll back through Slack or keep tabs on multiple channels, all I need to do is log in to Async and read the various posts folks have put up that mention me (if you're mentioned, it's important and you should probably read it) as well as other posts that might cover areas outside of my team that interest me.

It's a much more scalable approach than trying to read the backscroll in Slack, IMO.

It has a few special features, but on the whole it's basically like a company-wide journal.