If you work in an environment where the 'rules' are followed then yes, that works fine. Turn off the notifications and go about your task.

However, not everyone has that luxury. In my office, we are required to keep slack running. There are bullshit channels like #random, #memes, etc. that I have set to ignore. But then there are "Serious" channels where if the Boss speaks the expectation is complete participation.

    #General <Boss> I want to make all the icons a corn-flower blue across all of our sites.

--Now here is an example of the boss being an idiot and interrupting 30% of the staff. The accountants don't care, neither do the secretaries, the Help-desk, the Customer-support, or the SysAdmins. But because the idiot starts the conversation in the wrong fucking channel every damn reply and conversation that is sparked because of this interrupts me.

Incorrectly using the "tool" disrupts everybody who does use it correctly. If this was an email, it'd be safely ignored for 4+hrs. I'm not mad at Slack, I'm mad at corporate overlords who shouldn't even be allowed to touch a computer. But because Slack exists, I am forced to despise it.

I've got half a dozen other ways to send IM's to my co-workers. I never got interrupted in the past with bullshit like I do with Slack.