If you are using PayPal as your method of accepting payments and your shops version is less than RC2A, you need this contribution since the stock PayPal module has a basic flaw. Many times, a customer will place an order, be transferred to PayPal and then not return. This can result in lost orders as well as angry customers. With this contribution, that problem goes away. Some shops report problems with payments made with mobile devices when using this module. The Paypal App module is not prone to that problem and is the one we recommend for most shops.