Spinning up and down hard drives repeatedly drastically reduces their lifespan though. Once a day or so, fine, but if you set a 30 minute idle time or something and it spins them down a dozen times per day, you are putting acceleration forces on the drive many more times than intended.
If you have to buy a new HDD twice as often because you spin it down, any financial or environmental savings is instantly negated and in the end it is much, much worse in both respects.
Potverdorie?