The question makes me sound like an idiot, but I ask in more technical terms.

What does a body do, what is it's purpose?

The reasons I come up with are cosmetic purposes, protect passengers and the mechanics of a car from the environment, and for aerodynamics at high speeds.

Some cars do have monocoques which are the actual chassis of the car, but I am asking from the perspective of a tube frame chassis or traditional truck chassis.

So what else does a body do? What is it designed for? What are its uses?

Matt