In Joint Mode you can view Joints, i.e. bones that make up character skeleton.
A character in Joint Mode
Joint mode is rarely used for editing poses
Hiding and Showing Parts of a Character
In Joint Mode you can hide parts of a character model, if they make it inconvenient to work with a particular pose.
To hide an object, select it and press the V key.
By pressing Alt + V you can make all hidden objects visible again.
If you, for example, need to hide character’s arms, switch to the Joint Mode, select every bone in the arms and press V.
A part of the mesh will disappear. In the Node Mode, however, node controllers for this hidden part will be visible still.
If you want to hide them as well, select them and press V again. You can also use Mesh Mode to hide parts of the character clothing and other details like these.