Back in the day, there was this idea of some applications being "document" centered while others revolved around an "activity". On average you only want one ins

Back in the day, there was this idea of some applications being "document" centered while others revolved around an "activity". On average you only want one instance of your calculator application open as it's what you use to do math and having two or three might be confusing. On the other hand, when you use Microsoft Word there's really one window per a document and having five Word documents open at once make sense. This is another idea that has been somewhat lost over time. I believe the way it works now is that you can choose to have your application close when it's last window is closed, or not. That seems a reasonable compromise, it's never been clear to me why you'd want an application like Word with no window to continue running.