Wrist training will benefit these areas:
Chin Na (joint lock/manipulation)
Applying Chin Na
Resisting and counterattacking Chin Na
Striking
Resisting injury
Generating deeper and more penetrating power
Weapons
Swinging
Holding
Stabbing
Blocking/deflecting
Increasing flexibility/ range-of-motion
Improving endurance
Applying Jing (internal power manifestation)
Shuai Jiao (wrestling)
Grabbing
Throwing
Sealing
If your wrists get tired, even the most flawlessly executed techniques could become of little use to you. The beautiful movements associated with Chinese Kung Fu are worthless if your wrists are unable to handle the stress required to perform them. You should get to know the wrist, learn how it works, and understand what each part of the wrist is responsible for.