If this setting is enabled, XShutdown will attempt to automatically switch off your computer after shutdown has completed, instead of displaying the usual message that you may now switch off your computer.

This will only work if your computer supports this. For this, both your BIOS and your OS/2 must support at least Advanced Power Management (APM) V1.2. As far as I know, with OS/2 this is only the case for Warp 4 Fixpak 6 and higher.