You make a good point. I don't use this option. However, Windows users are used
to minimizing to the system tray and having things stay resident in memory
because real estate is limited due to having only one desktop. I suspect it is a
carry over from time spent in Windows. Just a guess.

With Alltray you can minimize any window to the system tray, such as Firefox.
However as you point out its usefulness is dubious. With the virtual desktops in
Linux, you can just keep them running and switch desktops, which is what I do. I
don't think it saves any RAM if they are minimized.