Heavywight windows vs lightwight windows

According to the Appcelerator documentation for Android there can be only lightweight and heavyweight Titanium windows. When navigation with heavyweight window we can close the corresponding activity by invoking win.close() method. My question is what happens to the full screen view in lightweight window mode when we navigate forward through the application? Is the view are automatically closed or should we have to manually close the windows by invoking win.close() method.