What's the purpose of having a 60-second timer for the shutdown dialog in macOS? Why automatically shut down the user's computer if they leave the dialog box open?
Ubuntu (Xubuntu at least) has something similar but 30 seconds. It's mainly an "are you sure" that doesn't prevent the user clicking shutdown and leaving the machine (what happens if you shut the lid of a laptop with this open? I'd expect it to shutdown rather than sleep on a mac). I (as an example) often hit save on a big piece of work, stand up, then hit shutdown and walk away, losing sight of the screen an instant after htting the button. Another user may tap the physical power button.
But it serves another purpose in this case. That checkbox for restoring the session. You have to have the chance to tick it. A less user-friendly approach would be to have a dialog box like
___________________________________ |Shut down | |---------------------------------| |Are you sure? | |[no] [yes] | |[yes, restore session next time] | |_________________________________|
without a timer. that gives you the same potions, except the impatient user comes back later to find the screen saying "are you sure?"
Though I do not use mac, I would take an educated guess, that the purpose of this is for, clearing active memory instruction runtime's, ending; operations, functions and tasks, shutting down the kernel, shutting down the gui, shutting down the system.
It is basically the same reason it takes time to boot up. You will never have a computer that just turns on in less then a second, all computers require time to boot up, and all computers require time to shut down.
The visual timer on the mac is a visual cue showing you how long till system shutdown.
That would be my guess anyway.