The recommended temperature for a typical computer system is 70 degrees Fahrenheit inside the computer itself.  Generally a computer is 10 degrees warmer inside the computer than the temperature outside the computer in the same room.

 

The disk drives, circuit boards, and power supplies all produce substantial amounts of heat, thus creating a build up of warm temperatures inside the computer.  Overheating inside the computer can cause the mechanical parts of a disk drive to work harder, and cause premature wear, and eventually failure.  Also, overheating can cause already warm components to become hot and possibly even melt, or burn out completely.