What is the purpose of the Audi A1's stop-start system?

I've noticed that my Audi A1 has a stop-start system that turns off the engine when I come to a stop. I'm wondering what the benefit of this feature is and if there are any potential downsides.

The stop-start system in your Audi A1 is designed to improve fuel efficiency and reduce emissions. By shutting off the engine when the car is stopped, it reduces unnecessary idling and saves fuel. However, in heavy traffic or frequent stop-and-go situations, the constant restarting of the engine can actually decrease overall fuel efficiency.