They probably get an unsolicited email every 10 days, just like I do, from slackbot, asking them to install the slack desktop client to get a "better experience," because someone at work added you to the slack channel. Only they don't realize that the slack desktop app is just a second web browser dedicated to going to slack.com, that they are running while they are presumably running their first web browser. Slackbot doesn't tell you that you are wasting compute having two browsers open, just that it's 'better' somehow than running the site on the browser you already have open. It also isn't very clear that once you have slack open, all your coworkers can see you are "available" like its 2001 and you are logging into AIM.
Even if they don't, I'd assume they would uninstall it as quick as they installed it when they start receiving notifications from colleagues during their break lunch or on the weekend. But it doesn't seem to be what the majority of people do. Not sure why people feel morally or socially obligated to keep checking what's going on at work on a 24/7 basis.
I wonder if there is a link with Twitter/Facebook/Instagram addictions.
I think slack knows a certain amount of people are like this, and have crafted the patterns in their product to maximize this behavior. That's why I get many notification emails a day that frequently leave out messages or repeat ones I've been sent already, to maximize my time checking the main client and be thinking of slack throughout the working day. Slack wants organizations to feel reliant on its services, even when it does little more in practice than email threads have done for my org at least.
I don't mind using resources on my personal device, I mind the access to my personal information. Carrying two phones vs. one for isolation make sense, but if the isolation can be done in hardware/software on the same device it's much easier for me.
I always ask why should I keep in touch with work during my private time. If it is really important, one could call my phone. If one does not bother to find my phone number, that means it is not urgent at all.