I agree that Slack fails as a structured discussion tool, but I find that having one giant notification repository with channels that anyone can subscribe to and filter is great. A server is down, someone is ordering food for lunch, a new customer signup with a premium plan, a competitor tweets something relevant, someone has a good joke, etc... Then unlike email it allows for a quick reaction and discussion on the topic. Also as a generalist I find that being able to have some notifications and sometimes participate without silos on marketing and sales topics (and reciprocally) pretty valuable, both for the company and my personal growth.