Widgets are double buffered by default, you can use this property to turn off the buffering. "Double buffered" simply means that Gdk.Window.BeginPaintRegion and Gdk.Window.EndPaint are called automatically around Widget.ExposeEvent events sent to the widget. Gdk.Window.BeginPaint diverts all drawing to a widget's window to an offscreen buffer, and Gdk.Window.EndPaint draws the buffer to the screen. The result is that users see the window update in one smooth step, and don't see individual graphics primitives being rendered.

In very simple terms, double buffered widgets don't flicker, so you would only use this property to turn off double buffering if you had special needs and really knew what you were doing.