See OS X Animations in Slow Motion – Mac Kung Fu, 2nd Edition

Tip 304See OS X Animations in Slow Motion

Holding down Shift while clicking just about anything in OS X that uses an animated transition will reveal the animation in slow motion. For example, holding down Shift while minimizing a window to the Dock will slow the minimizing process in pleasing slow motion. Holding down Shift while activating Mission Control using the keyboard hotkey will do the same.

This feature was added to OS X to allow former Apple CEO Steve Jobs to demonstrate the beauty of window animations while giving the first keynote speech introducing Mac OS X. It has hung around in the decade since!