Richfaces is one of many JSF component libraries out there. The benefits of using any JSF component library (Richfaces, Icefaces, Primefaces, etc...) is that you get a feature rich control set with a good deal of AJAX functionality built into many of its controls.
I personally use and prefer Primefaces as it seems to have the most feature rich controls however it can be buggy. Richfaces isn't as nice in my opinion but it seems more stable.
Check out the demos to see for yourself what they have to offer because they come with a lot of functionality out of box.
http://www.jboss.org/richfaces/demos
http://www.primefaces.org/showcase-labs/ui/home.jsf