Leave it on or turn it off?  This question has been around since desktop and personal computers started to make their way into offices and homes.  Computer hardware has improved a lot since the early 1990s.  Most of the old procedures really no longer apply, but many hold on to them.  Many insurance policies now have electrical surge protection provided.  One of my customers in Florida has just received $500 for an electrical surge that burned many components inside her computer.

Apple computers run maintenance procedures once a night, once a week and once a month.  Knowing this, I put my Apple computers to “sleep” every night when I am done with them for the day.  Every Sunday I shut them off for several hours then boot them.

Computers running Windows like to be turned off.  Depending on which Windows operating systems you are using, Windows 95, Millennium, 2000, XP home, XP Pro, or Vista each perform different procedures when they are turned off.  At the end of the day I turn all computers with Windows off.  

Laptops need their batteries exercised to help the battery last as long as possible.  Once a week unplug your laptop and use the computer until 2 percent is left.  At this point save all your work and turn the computer off.  Let the battery rest for several hours then plug it in.  Let it charge overnight if possible.  This allows the battery to charge the rest and recover from being used. 

The bottom line is that both side of this question can be supported.  If you are a desktop user do what you think is best for your situation.  If you are a laptop user you need to exercise the battery.