Turn off that computer!
Electronics have a limited lifetime. If you are not using your computer, turn it off. The energy saved could save you $20 a month. This will also decrease the possibility of data loss. The longer your hard drive is spinning the more likely it will fail. You could save your electronics from damage from a storm. There are a number of good reasons to just turn it off.
A computer is a space heater. If it's a hot summer day and you're not using the computer it is working against your air conditioner. It takes over twice as much energy to remove heat from a room than the energy used to create the heat. This means that if your computer is using 400 Watts it takes 800 Watts of electricity to run the air conditioner to cool the air. Now you have wasted 1.2kW. After one hour of the electricity used it could cost over a dime. This waste of energy now over a night can cost over a dollar.
The downside to turning your electronics on an off is always electric shock. The spin up on the motor shortens the live span of a hard drive. However, with the lifetime saved by not running it, your hard drive will still last as long. Poorly designed electronics will not survive turning them off and on frequently. Most manufacturers seem to forget to reinforce any suppression electronics. This is a common reason why most power supplies fail. Electronic surges from turning electronics on and back EMF from turning them off. The electronics are not designed to handle the increase in voltage seen from these events and will slowly degrade the semiconductor devices and damage the electrolytic capacitors.
Yes, your junk electronics may fail quicker, but your good electronics will last longer and save you money.