Allowing you to find deals on your smartphone screen, pick up and purchase them, and providing an on-screen redemption code for the retailer, there's no real need to leave the app to find the deals in your area.
From the Marketplace description:
Save up to 70% on daily deals in a city near you! The Groupon app unlocks the secrets to living your city for less. Get exclusive discounts on restaurants, shops, spas, days out, and so much more with this cool little app. Download it now to see today’s deal.