Turning Off the Computer

[bruce12borland-H+0wwilmMs3R7s880joybQ at public.gmane.org (Bruce Borland)]

The other night I asked my son to turn off the computer.  He apparently 
did not want to wait for the computer to shut down normally, so he 
decided to switch off the power to the machine, stopping it immediately. 
 I told him that was not good to do, but he asked me why.  I did not 
have an answer for him.  He did this to our Windows machine, but I 
understand that it is not good to turn off a Linux machine this way 
either.  Can someone explain what problems are caused by such an 
immediate shutdown?  I would like to know, and would like to tell my 
son, too.  Thanks.

Bruce Borland