It handles functions related to the position, orientation and scaling. Both vtkActor and vtkVolume are specializations of class vtkProp . This is the point about which all rotations take place.
Visibility is like a light switch for Props.
Use it to turn them on or off. Also see dragable. This is typically done through an interactive mouse interface. This does not affect methods such as SetPosition, which will continue to work. It is just intended to prevent some Props from being dragged from within a user interface.