I just don't want to have to forward to a url every time I want to use a servlet that does processing. In asp there was a way that you could execute another asp page (like a servlet), passing it the request/response objects, but never leave the page you're on. That means you don't have to make a trip out to the browser. If I have a servlet that does some good stuff and can be hit either by URL or by just processing, I could do:
//IN MY
JSP PAGE
getServlet( "DBServlet" ).doPost( ... );
//NEVER LEFT SO CAN FINISH
//NO ERROR THROWN, EVERYTHING OK...
out.println( blah, blah...);
Also, I can have a DB servlet that has DB sepcific methods I can use as well as the doPost/get methods. I see tons of uses for this.