Camera rigs come in a range of shapes and sizes to support different cameras and different shooting applications.
Camera Cages and shoulder rigs are both designed to smooth out your footage and improve the production quality. Smooth footage gets out of the way of the message. Footage that is not smooth distracts the veiwer from the message you are trying to convey.
Cages allow more portability, while shoulder rigs provide more stability. Which is best depends on what you want to shoot.