Its perfectly legal and does not violate the spec. One obvioous advantage of this is that the compiler can catch you if the bean class and the component interface do not implement the same set of methods. But this is not that much of an advantage because most
IDE's will catch you for this at deployment time. That's why people do not use this configuration mostly. It's very rare to see an
EJB designed this way. Another advantage is you could reuse the business interface.