One thing even private organizations should think about is the potential for chats on Slack to embarrass the heck out of them. Slack doesn't let an organization

One thing even private organizations should think about is the potential for chats on Slack to embarrass the heck out of them. Slack doesn't let an organization sunset and delete private chats/DMs after a certain amount of time. When employees think they aren't overheard they start to get very frank with each other (which is good, I think frank and direct communication is important). But sometimes they say things that are ignorant or even their frankness can reveal things about the company that are embarrassing. This isn't even a theoretical scenario anymore, look no further than dumps from recent hacks. I like Slack's default-to team member privacy but you can implement these features without compromising that. I opened a case with Slack about it but they closed it with the standard "consider it in the future" response that I expected (which I don't hold against them, I can't say I wouldn't have done the same). It may take a breach of Slack's infrastructure and subsequent leak of private chats for them to make the changes needed for organizations to protect themselves from this. It might only take user education to protect a company from this, but in the end if you're a big enough organization there are going to be people that don't care, hate the organization or are just to jaded to take the ramifications seriously.