In some situations you may have to shut down and restart Windows very quickly. This would be an emergency restart. An emergency restart if basically just a forced restart without a timeout. (ex: shutdown.exe -R -T 00 -F)
An emergency restart can be helpful in circumstances when you cannot normally restart your computer, and is much better than turning off the power to your computer by performing a hard restart (reboot) which can be harmful to the computer.
This tutorial will show you how to perform an emergency restart as needed in Vista, Windows 7, and Windows 8.