That's interesting. We've played with a couple integrations but don't use any. What sort of org are you in? We're an academic bioinformatics lab with 15-20 people.
Not OP, but we have numerous integrations. Technical, corporate, and fun. GitHub, Jira, Status Hero, Outlook Calendar, Asana, Conference Booking, polls, "water cooler" type apps, and more. I actually can't get a comprehensive list right now because Slack is down...
We could make do without many of these integrations if we had to but the integrations and webhooks are THE killer feature to me. Chat is easy to solve.
FWIW, some of the hosted Slack alternatives, like Zulip, support at least versions of some of these -- see their integrations page here: https://zulip.com/integrations/
What would be ideal from this perspective would be if they could make the integrations somehow code-compatible with Slack, but that's tough. For example, Zulip's topic system is, IMHO, vastly superior to Slack's threads, but every public message is under some topic (within a stream -- there are two levels, not one), everything posting a public message has to supply one, and that alone might make it difficult to reuse a Slack integration unaltered.
We could make do without many of these integrations if we had to but the integrations and webhooks are THE killer feature to me. Chat is easy to solve.