Prevents users or applications from changing the visual style of the windows and buttons displayed on their screens. When ...

Prevents users or applications from changing the visual style of the windows and buttons displayed on their screens.

When enabled on Windows XP, this setting disables the "Windows and buttons" drop-down list on the Appearance tab in Display Properties.

When enabled on Windows XP and later systems, this setting prevents users and applications from changing the visual style through the command line.  Also, a user may not apply a different visual style when changing themes.