In-dock notifications and system notifications are my reasons, as well as a dedicated window I can alt-tab to instead of tabbing through browser windows, then navigating to the Slack tab.
(I realize that for some people, "hiding" Slack in a pinned tab may be a feature.)
If you are happy, no problem. I'm posting for general info.
It does. In fact, it keeps displaying an annoying blue-colored topbar telling you that your life will be better if you enable notifications (fortunately, with the option to snooze it or dismiss it completely on given machine).
Emacs-slack can get you all of that:-)
I know, it's a minor kvetch. But it's a minor kvetch I can solve with a gig of RAM.