Not even for companies, IRC IMO would be much better, the only issue is, as always, you need someone responsible for the infrastructure: not only servers, but scripting for Jira/Dropbox/NameYourCurrentTrendyPlatform integration.
-No single point of failure.
-No dependency on a different company for a vital points of your business.
-No private info stored on a 3rd party system, in a different state and potentially a different country (legal nightmare to ask for damages).
-Distributed system. Local servers give lower lag for multisite companies, internet access outage means netsplit, not inability to communicate.
-Already existing indexing and searching features if desired.
-Many bots to automate/notify/interact with insane amounts of stuff.
-Thousands of IRC clients, with enormous customizing features, for every conceivable platform, that do as much and even more than all these "this is how communication should be" solutions.
-Bridging IRC to XMPP/Sametime/etc plugins/apps to interoperate with other companies.
I can sort of understand Slack for a small company, but if you have your own server infrastructure, no, I can't.