Note that RISC OS had to contend with running off floppy disks too. So you might start one application off one floppy disk, and the next off another, and you'd have them both in ram, but neither had any data in them yet, because that might come of a third floppy disk.
That's at least one concrete scenario where "application loaded" need not be the same thing as "having data open in a window".
It's been a while though. I just know they were extremely consistent in keeping the distinction between "application loaded" on one hand and opening a window on the other (or taking over the screen, in games) . This does help with your mental model of where your RAM is going, since you have a limited amount of it. Closing applications might free up ram you need for something, but now you might need to juggle floppies again. And so it went.
ppps
Also, windows (and some of mac os) seems to confuse opening a file with opening an application. It's not the same thing. An application can have 0, 1, or infinity files open in memory at any one time. "Why the heck does eg ms windows always open nonsensical empty windows when there's nothing to show?" I'm not sure it's a hill I'd die on today, but I used to have Opinions on this! "The window is not the application, an application can have lots of windows!" (Ha, you're reminding me of old rants back from decades ago ;-) )
I think the part I keep forgetting is the "Menu" mouse button. In the RISC OS case, having the application icon in the Icon Bar is, effectively, like having the application "foreground and running." A "Menu"-click on the icon parallels having, say, a MacOS 7.5 application running with its menu visible at the top of the screen. The Mac puts it more "in your face" but either way the ability to open the application menu and start a new document is essentially equivalent in both cases.
I'm reminded of the utility !Menon that I used to keep track of all my important files across many floppies, once upon a time. No window at all IIRC. Just drag and drop, and the Menu button.
Note that RISC OS had to contend with running off floppy disks too. So you might start one application off one floppy disk, and the next off another, and you'd have them both in ram, but neither had any data in them yet, because that might come of a third floppy disk.
That's at least one concrete scenario where "application loaded" need not be the same thing as "having data open in a window".
It's been a while though. I just know they were extremely consistent in keeping the distinction between "application loaded" on one hand and opening a window on the other (or taking over the screen, in games) . This does help with your mental model of where your RAM is going, since you have a limited amount of it. Closing applications might free up ram you need for something, but now you might need to juggle floppies again. And so it went.
ppps
Also, windows (and some of mac os) seems to confuse opening a file with opening an application. It's not the same thing. An application can have 0, 1, or infinity files open in memory at any one time. "Why the heck does eg ms windows always open nonsensical empty windows when there's nothing to show?" I'm not sure it's a hill I'd die on today, but I used to have Opinions on this! "The window is not the application, an application can have lots of windows!" (Ha, you're reminding me of old rants back from decades ago ;-) )