In my case I'm a bit more cursor centric than keyboard for this use case. I use all the keyboard commands for the normal, cut, copy, paste, print, save, etc. but when a new window or dialog opens my hand reflexively goes for the mouse (trackpads aren't my thing). At which point I'll be moving or resizing a window or clicking a particular button in the dialog. But a lot of the time the window or dialog opens up halfway across the screen, or in the case of some apps, in the middle of the screen or on another display.
I know what you're going to say, "Well then, just retrain yourself to use the keyboard" and my reply will be "Because I don't wanna". This computer is here to serve me, not the other way around.