1) real-time remote communication - email works for most situations, but due to the async nature sometimes you want to resolve something quickly (e.g a customer

1) real-time remote communication - email works for most situations, but due to the async nature sometimes you want to resolve something quickly (e.g a customer issue) and a real-time chat is a better medium. Video chat is a bit heavy, because it requires scheduling, coordination etc where chat is "always on", and doesn't require you to prep for a video call. 2) user experience - IRC existed for decades before Slack and does most of the same functionality, but the UX is cumbersome for your average user. What client do I use? What server do I join? What channels do I join? How do I use /commands? How do I get it on mobile? Slack "just works", you sign in with your work account and everything is there, ready to go.