Frankly, I prefer never to have my hard drive go to sleep. Just as in an auto, where going from 0 to 60MPH to enter a highway causes a lot more wear and tear on the engine and uses a lot more gasoline than keeping the car moving at a steady 60MPH (think about how much more you press the gas pedal when accelerating than when just maintain speed), every time your drive sleeps, its disk comes to a complete halt. Every time it wakes, it must very quickly spin up from 0 RPM to 5400 or 7200RPM…which uses much more electricity than just keeping it spinning at its normal speed, and puts much more stress on the drive motor that spins the disk.

The concept of drive sleep was originally conceived when older drives used much more power than they do now. Sleeping a disk saves you extremely little in energy costs, but costs you much more when you have to replace the drive prematurely. Let the drive spin all the time. It will last longer, and even though you might pay a few cents more for electricity over the drive's lifetime, you'll actually save you money in the long run.