The Shutdown Event Tracker was created to give a better impression of why the computer is shutdown/restarted, by forcing the user to add a comment about why the shutdown is needed. The Event Log will then contain documentation of what changes that have been applied to the system, which required a shutdown.

This can be useful for the Administrator, but can be an annoyance for the home user, so it is possible to configure whether one should give a reason for shutting down:

[HKEY_LOCAL_MACHINE \SOFTWARE \Policies \Microsoft \Windows NT \Reliability]
ShutdownReasonOn = 0 (WinXP Default = 0, Win2k3 Default = 1)

Note the Win2k3 Resource Kit includes the Custom Reason Editor (Custreasonedit.exe), that allows one to add/change/remove custom reasons for shutting down.

More Info MS KB293814

Credits sanx.org