The system window was handy for retrieving windows that had somehow ended up offscreen. Alt-space, M for move, hit an arrow key once, and then the window follows your cursor and ends up on screen by default. Still works in modern versions of Windows - it's somewhat obsolete now you can use Win+arrow keys to move a window around, but it might still be useful if your window has ended up somewhere and you can't figure out where.
Imperfect graphics drivers and an environment that changes screens and resolutions a lot means that once every few months some fucking application is going to wander off where I can't get to it, and no amount of Windows+directionkey will move it somewhere usable.
The system window was handy for retrieving windows that had somehow ended up offscreen. Alt-space, M for move, hit an arrow key once, and then the window follows your cursor and ends up on screen by default. Still works in modern versions of Windows - it's somewhat obsolete now you can use Win+arrow keys to move a window around, but it might still be useful if your window has ended up somewhere and you can't figure out where.