No! It saves energy and extends the life of your computer. Turn your computer off when not in use if this will not interfere with automatically scheduled backups or updates. It does not hurt the computer to be shutdown and powered off.

Contrary to popular belief, turning on and off the computer doesn't shorten its life. The belief that frequent shutdowns [of PCs] are harmful persists from the old days when hard disks did not automatically park their heads when shut off; frequent on-off cycling could damage such hard disks. Modern hard disks are not significantly affected by frequent shut-downs. Shutting down computers at night and on weekends saves significant energy without affecting the performance. So, if you are going to be away from the computer for several hours, turn it off! Your computer cannot be infected or invaded when it is not connected to the network. If you haven't turned on your computer in a few days, be sure to check for updates for software and anti virus files before you do anything else.

If you must leave your computer on for backups or updates, then turn off the monitor. Turning off the monitor (CRT) will not affect the program that is running, but will save 50 to 75 per cent of the total energy required to run the computer. Even on the modern LCD flat screen monitors you can save up to 25 per cent. These savings can be compounded. Shutting down computers when not needed reduces heat generation, which in turn cuts back the need for air conditioning."