What are the benefits of using a Stateless Session Bean over using a class purely consisting of static methods?
One common use of Stateless Session Beans is to implement a facade over a set of entity beans, in order to allow the client to be transaction-ignorant. In this pattern the session bean defines a set of transactions that it implements using entity beans. See FAQ question "What is the Session wraps Entity Pattern? What are the motivations behind it?" for more information.