Internal Kung Fu, and Tai Chi in particular, has many health benefits. The nature of these styles is that they work to strengthen the body from the inside out and focus on harmonizing with the natural movements of the body. It incorporates skeletal alignment with strengthening of the tendons to improve the body's framework. Movements done through relaxation open up chi meridians.
This allows energies to flow naturally through the body improving the immune system, generating calmness, confidence and peace of mind while reducing stress, depression and chronic pain. It also works to improve muscle tone and general physical fitness overall. It helps with balance and coordination, focus, and a clear mind. Many people use Tai Chi as therapy and the health benefits are well documented.
Below are some links to articles that go into greater detail about the benefits of Tai Chi.