Every company at the conference was an example of the effectiveness of growth teams. Facebook, LinkedIn, Zynga, Twitter and so on have all found that being rigorous about optimizing their growth models has increased growth and engagement.
They were also at pains to mention that you cannot A/B test your way to a great product. You need deep insight and intuition to build a great product. But once you have a great product, you can help it grow faster by being rigorous about optimizing the drivers of growth.