Hibernate & Spring

From http://static.springframework.org/spring/docs/2.0.x/reference/orm.html#orm-jpa

The LoadTimeWeaver interface is a Spring-provided class that allows JPA ClassTransformer instances to be plugged in a specific manner depending on the environment (web container/application server)

When is load time weaving required?

Not all JPA providers impose the need of a JDK agent (Hibernate being an example). If your provider does not require an agent or you have other alternatives (for example applying enhancements at build time through a custom compiler or an ant task) the load time weaver should not be used.