counterpoint - Sometimes I do this for myself to prompt myself into a reply when I'm finding it hard to compose the message. Once I've said something, no matter how small, I know I have to follow up within in a couple of minutes. It's like a kind of short-term Ulysses pact.

Also I'd say this depends on your existing work culture - I've been in places where the expectation is that everyone has Slack messages muted. If anything was really that time sensitive it's still possible to pick up the phone.