One reason is to be able to close the last window of an app without quitting it. Always bugged me how on windows, if I closed, say, the only word doc I had open, I had to relaunch word again (with all the loading time that that entailed) just to open a new doc. On a Mac you can close windows without worrying that you're also going to quit the app (except for apps that only support one window, although I do think itβs silly that every app doesn't just support multiple windows).
Why the app has to be scrubbed from memory immediately after you close the last window? We are not in the times with 512kb of RAM memory. This is not something that the user should have to worry about today.
This is the simplest caching scenario I can think of.
