As you said, scrolling under pointer is a huge boon, but also clicking on background windows (in most well-behaved apps) usually focuses the window without sending the click to the window (possibly triggering an unintended destructive action).
But the best part is that cmd-click allows interacting with windows without focusing them, allowing all sorts of things like translating your IM window out from under a movie player without covering the video.
I didn't know cmd+click. I can't think of a good use case in my world, but I'm pleased as punch that it exists, and that I've learned something new about OSX today.
As you said, scrolling under pointer is a huge boon, but also clicking on background windows (in most well-behaved apps) usually focuses the window without sending the click to the window (possibly triggering an unintended destructive action).
But the best part is that cmd-click allows interacting with windows without focusing them, allowing all sorts of things like translating your IM window out from under a movie player without covering the video.