Not very good when the VRDB is generated automatically as in the Screensaver or when System is Idle. These could well run whilst the system is in use just that at that time the screensaver is running or is temporarily idle and you wouldn't want it to shut down in that circumstance.
Personally I don't want 'anything' to shut down windows, I will control when my system shuts down, a system in power saving standby or hibernation really doesn't use that much power.
