Does that reduce the ram footprint and the slowness of the thing, or does it just mean the task manager/system resource monitor files it under "Firefox" instead of "Slack"?
(I write and dislike web apps since I tend to lose them. Having dedicated windows which don't host all the links I click on to documents is much more conducive to my organisation style. Actually, I would go so far as to say that I wish web browsers would still let you turn tabs off.)
For me, its not about the resource consumption of my computer, its about my personal resource consumption. Keeping it away from my taskbar (on an entirely different workspace, in fact) helps keep it from being an excessive interrupter.
Also means that I never have to see the unread message notification if there's no icon for the Slack app in my Dock or Cmd + Tab.
No other notifications enabled. I tab over to Slack when I'm in a time and space that I can respond to questions.