IF Graffito is running outside Jetspeed 2, this engine has to be used in order to setup the Graffito components.
The engine can be a static class in an EJB session bean or other kind of J2EE server components like servlet, ...

If you plan to use Graffito inside Jetspeed 2, there is no needs to instantiate this engine. 
See in the getting startup page to know how to deploy Graffito into Jetspeed 2.