The default value is false.
When this property is at it's default value of false, the UIKit.UIViewController's UIViewController.View's UIView.Frame is sized so that it does not include the area under the device's status bar (the area at the stop of the screen that shows, e.g., signal and carrier, battery charge, etc.). If set to true and UIApplication.StatusBarStyle is set to UIStatusBarStyle.BlackTranslucent, the UIViewController.View will be visible behind the status bar.
C# Example
public override void ViewDidLoad ()
{
base.ViewDidLoad ();
WantsFullScreenLayout = true;
UIApplication.SharedApplication.StatusBarStyle = UIStatusBarStyle.BlackTranslucent;
}