What is a cervical discography study good for?

Discogenic pain. When patient complain neck pain without radiation to the arms and the source of pain is thought to be the degenerating disc, not the joints or ligament or muscles---then it is time to do discography to try to prove the disc is the source of pain.
Confirming painful d. Confirm suspected painful neck disc as pain generator prior to a surgical removal and fusion or replacement part of a complete evaluation for axial neck pain. Its usefulness is debated.