The effectswhich include the spinning cube and other desktop workspace-switching animations, animated icons, and animations for windows that show what state they're inare just plain cool-looking and add to the ultramodern look of the KDE4.2.2. UI.
Netbook users and anyone else who has a slow CPU or GPU should turn this off (it is on by default)at least when you're running it on battery. They're CPU/GPU-intensive.
While the spinning cube is a cool desktop switcher, I suspect if I left it on, my battery life would be one hour or less; not three hours or so. Access this via System Settings > Desktop icon > Enable Desktop effects.