Maybe I'm just overly paranoid but I've never understood the appeal of Slack - I personally don't want to ship all of my internal proprietary business communications offsite to a third party.
I think it really depends on what your team needs to discuss, but from my slack chats we don't discuss any business-breaking proprietary intel. If there's something important a face-to-face meeting is used or video chat (but that's also through hangouts)
