Specifically as a developer, but more broadly any time you’re involved in deep work, having notifications on for anything (slack, email, social media, etc.) while you work is unprofessional.
If you’re a manager, and your primary function is coordinating between people, this does not apply. But if you are in a role where focused work is required, this is true.
It's well-established that when developers get interrupted, it takes time to get back into “the zone.” When you are working on a problem, you’re building a mental model of all the different things you are interacting with. It’s a fragile balance in your head, and when you get interrupted you get snapped out of that focus state.
It’s very common to have notifications. You think that at the very least, you need to be on Slack to be connected to the team. But as a developer, your most important job is to do the actual development work.
Sure, you have to help other teammates, but that is not your primary function. Sure, responsiveness is important, but responsiveness within a few hours is different than responsiveness within a few minutes.
Focus on the job at hand and silence notifications while you work.