When you enable "Limit window proportions on resize", there are no additional black bars on the sides or top and bottom.
When you enable "Snap to desktop edges", well, it snaps to the desktop edges when you put it nearby, but you can also put it off-screen if you want to.
I currently put in that extra-effort to precisely resize and place the pop-out video frame on the bottom right corner of my screen. I wish this wasn't necessary.