MoveIT Package for an Industrial Robot

I was following the [tutorial](http://wiki.ros.org/Industrial/Tutorials/Create_a_MoveIt_Pkg_for_an_Industrial_Robot) on using the `MoveIt Setup Assistant` to create a MoveIt package for an industrial Robot. In the Add Planning groups section, it is mentioned that adding a Kinematic Chain is generally preferred over add joints or add links. But in [this](http://docs.ros.org/indigo/api/moveit_tutorials/html/doc/setup_assistant/setup_assistant_tutorial.html) MoveIt tutorial, they use the Add Joints for the planning group `right_arm` and Add Links for the `right_gripper` group. I want to know what is the difference between these two approaches. Which one is better and in what situation? Thanks for all inputs!