Typical computer costs about $6.00 per month to run 24/7/365.
Most components, just like an incandescent light bulb, suffer from thermal damage when turned on/off repeatedly. It is the warming up, and component expansion from going to operating temperature, then the cooling to room temperature, that stresses all the Integrated Circuits transister junctions.
The original Edison Light Bulb in the Edison museum has been ON for 100 years. How long do yours last?
Most electrical components seem to fail when powering up. Having been a technician on large aircraft, mobile communications and computing systems, Air Force Rat Rigs -Radio and Teletype mobile shelters, and vehicle electronics, for over 41 years, has taught me this on a recurring basis.
In my home, I have two computers that are on 24/7/365. The others, up to 12 or so, never all 80 at one time, get spun up when all the kids come over to learn Linux and gaming.
http://pclinuxos.com has 1900 FREE games and programs, crashfree. So, they, unlike the Microsoft systems, can run indefinitely.
Maybe that is why Microsoft.com, Hotmail.com, MSN.com, joined their 45,000 servers with the Fortune 1,000 companies, and the other 76% of the Internet, in running the Linux on all their computers? Uptimes for Microsoft servers can be up to 14 days, by all experienced Web SysAdmins. Linux is 'forever'!