If I don't think some company's messenger application should run in the background on startup, it should not run in the background on startup.
There are many people who need more personal discipline to not contact people constantly, but the software itself should be ready for the times when they should contact you, interrupting whatever it is you were doing.
For the majority of people it makes sense to have a comms app always running as they come to expect that from the smartphones.
Granted, there should be an easy way to configure this behavior for advanced users.
In contrast, I see a computer as a general purpose machine. Sure, I don't turn off the WiFi of my laptop, or the router/AP from my house, but those are means to many ends. When I want to check mails on my computer, I launch Thunderbird, and when I want instant mesaaging, I use whatever program/WebApp I need.
[0] As I am now doing, writing a comment in HN is a PITA in a smartphone.
Same thing with Signal. I routinely take/place calls with friends and family through the desktop client. If I'm on my computer and I've got my computer headset on, I might as well take the call on the computer instead of taking off the headset and using yet another device.
As my computer is a general purpose device, one of its many purposes is also a communications device.
Or do you leave it connected for long stretches of time to be ready to take an incoming call?
If you had a desk phone did you unplug it until you were going to make a call?
That would be a slightly different way of accomplishing what I already do (silence everything on my phone, and in general, try to prevent it from bugging me when I'm not actively using it).
It wouldn't be a bad approach at all if it made the phone shut the fuck up. The smartphone is one of the best examples on the market of product managers mistaking addiction triggers and "engagement" metrics for evidence of good user experience.
Yes, I do (effectively). My phone spends a large percentage of the day in airplane mode.