Honestly, if you look in activity monitor there are over a hundred apps running without any windows being rendered.
Maybe it’s because I’ve always had more ram than I need?
Of course you can close the app manually, but that is cumbersome: You close every window with command-W or a click, but have to remember to close the very last window with command-Q. If you select the app icon to quit, it will not just activate the app, but open a new Window. So the best way is to right click the dock icon and close. But then you have to think if there is still an window open or not, so you don't accidentially close it.
It's not a big deal, but it is a slight annoyance, just like how you can't close minimized windows. Apple actually implemented auto quitting apps in the Lion era, but removed it (probably because it was to Windowsy?).
macOS applications can still choose to close the app automatically when the last windows closes:
https://developer.apple.com/documentation/appkit/nsapplicati...
Disclaimer: Mac is my main platform since around 2010, before that Windows, and before that Amiga - one would think that more than a decade would be enough to acclimate, but the whole application model on Mac still feels weird :)
To create a new document window if you need it.
It looks like this app just sends a request to terminate (AppKit.NSRunningApplication.terminate()) to any app with no open windows (after a delay). If the app is already ready to terminate (termination counter is 0), most of the terminate work has likely already been done, and the app will probably just get killed. If the app isn't ready to terminate, invoking terminate is going to cause it to wake up and do whatever its own processes for terminating might be. For something lumbering and bloated like an Adobe app, this is going to be a ton of stuff. For modern macOS apps with good support for sudden termination/automatic termination, this is probably little or nothing at all.
So for apps that work well on macOS, this accomplishes little more than removing the icon from the dock and the app switcher. For apps that don't work well on macOS, this might or might not help things work any better.
With other operating systems, maybe quitting unused apps is worthwhile for performance or battery life or whatever. And some applications on the Mac, like (unfortunately) Excel, don't cooperate as well as they could with OS resource management, so quitting them when you're not using them is probably good. Otherwise, a modern macOS app that goes idle is going to be compressed and paged out and suspended so that it's not really soaking up any resources if it's not doing anything (even if it has windows and documents open, incidentally).
So, sure, quit apps with no open windows if you just want a tidy dock and app switcher. Unless I'm missing something, I think that might be all you're really getting.
Just because you can stand on your right leg doesn’t mean your left leg is useless. Learning to work with keyboard shortcuts together with your point-and-click skills will make you more efficient.
(macOS can't discern between apps I shut off manually before a restart and apps the OS shut off for the restart, so it ends up opening everything anyway.)
I guess windows users?