So why would you need slack then in the first place?

You don't, but have little choice when it's foisted on you.

If you're a knowledge/tech company, would you let me put a device in your worker's workspace that emitted an annoying noise randomly ever 5-15 minutes, interrupting them and causing them to spend time regaining their focus on that ask they were working on? Probably not, but orgs are handing money over hand over fist to Slack for the privilege of enabling this.

Knowledge Productivity Diagram Example: https://i.imgur.com/sAdZ63y.jpg

Because it's the standard for communication at your company. I don't mind Slack, but I have co-workers who hate it, but don't really have a choice but to use it at least occasionally.

Because you can catch up during breathers / breaks from your main task.

I actually really like slack for casual conversation, for non-blocking work comms, and for general info, I only dislike when folks expect urgent responses via slack. So I've adjusted my slack config to make it work wonderfully for the use case I prefer, and to work around the use case I don't.

or you can just close the app