What is the purpose of the Audi A7's start-stop system?

I'm looking to purchase an Audi A7 and noticed it has a start-stop system. What exactly does this feature do and how does it work?

The Audi A7's start-stop system automatically shuts off the engine when the car comes to a complete stop, such as at a traffic light. This helps to reduce fuel consumption, emissions, and engine wear.

In addition to saving fuel and reducing emissions, the start-stop system also helps to reduce noise pollution in urban areas by shutting off the engine and providing a quieter environment.