It shows Google Checkout customers more relevant information in Google search results by displaying the Google Checkout badge on the sponsored links of merchants that offer Google Checkout.
In order to simplify the buying process. Google Checkout provides customers with a single checkout mechanism, so you don't have to share your credit card details with every store you purchase from. A single login is all you need for use across multiple stores.
You can keep track of all your purchase in one place at Google.