Stage Object
The Stage object acts like a movie director. It determines when a camera, an environment, a background, etc. are used within an animation.
For example, you can create many different cameras in your scene and use the Stage object to decide when to cut to a particular camera.
You can also use the Stage object to switch between Sky, Foreground, Background, and Environment objects.
To assign an object to the Stage object, Drag & drop a Camera, Sky, Foreground, Background or Environment object from the Object Manager into the appropriate box.
As can be done with all other objects in the Object Manager, the Stage Object can be activated and deactivated using the green check mark and red x, respectively. This lets you, for example, render the scene from any angle, even if the animation switches from one camera to another, without having to use one of the Stage Object's predefined cameras.
The Stage object can, by the way, be enabled or disabled via the green and red crosses, respectively, as is the case with other objects. This, for example, to render any view despite having multiple animated camera changes without having to use the cameras defined in the Stage object.