|Of course there is a reason.|
My UPS is scheduled to power off at 10:00pm and to power on at 6:00am.
If the computer was shutdown and powered off, it will not power on automatically when the UPS restore the power.
I did that before with Windows NT4. But now, I have a new system, Windows Server 2008 ans Small Business Server 2011, and I don't know how to let the system shutdown without power off.