Car Demo Question

Questions & Answers
1

"For various reasons, we want the car to be in its own layer. With the Car GameObject selected, go to the Inspector and select car in the layers drop down menu. In the popup menu click Yes, change children to make the change apply to all GameObjects in the cars hierarchy."

WHy do we want the car to be on it's own layer?

2

http://unity3d.com/support/documentation/Components/Layers.html

They probably want to be able to run custom lighting and FX on the car model. It also means you could add motion blur to everything but the car. I'm only guessing here though.