The product feed is an XML file contains information about your products. By this file, you provide that information to search engines. Google uses it to index pages on your site. Thus you provide a quick and easy way to add your goods in Google Product Search results.
Furthermore, many sites for price comparison and e-commerce using a product feeds. Thanks to them, they update their database with the items you offer.
In this article, I describe several techniques that will be useful in optimising your feed. That will increase your sales and profit.