I don't like to have to remember too many shortcuts to do the same thing. The one works both places and if you have some app like calculator, To do or Sticky Note up on your desktop Alt F4 will have to close each individually before it shuts down, so you would have to Alt F4 several times whereas with CTL ALT DEL it is just one time.

Bonus - If you are loading a small app automatically at boot like a sticky Note on your desktop, guess what, you boot directly to desktop.