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.

Your boss sounds pretty bad. I doubt you’re going to have a good time with any set of tools.

The problem isn't the tool, it's the boss.

Just have every channel on mute (apart from your co-workers).

If your boss insisted you could have a computer but had to use an on screen keyboard, you wouldn't complain the computer was bad. Same with slack.

But turning off notifications is not using the tool right. The fact that you have to turn off notifications indicates that most people use it incorrectly (e.g., @channel/@here-ing for super unimportant messages).

Slack does a really poor job of guiding its users to use the tool properly. There is no warning when someone decides to @here the #announcements channel with 200+ people to wish someone a happy birthday. That's poor design.

If you can't opt out of it completely, that means that there is some socially-determined expectation as to how responsive you're going to be. Not everyone can unilaterally set their own level of responsiveness without a negative impact on their standing in the company.

That's exactly my point, but you need to be in a company where that's an acceptable thing to do. I'm lucky to work in a company where "I'm sorry, I was offline getting stuck into some work" is a very reasonable response, but it seems like much of the criticism of Slack comes from companies where that's not possible, or people who don't have the discipline to actually log off (which I am definitely guilty of at times!).