The benefits of chi kung has many layers - just like an onion, as you remove one layer a deeper layer presents itself.
At a basic level chi kung greatly improves your body awareness, breathing, posture and opens up the joints, relaxes muscles and relieves stress and aids digestion. These 'advantages' are great and felt very quickly and because of this people think that is it!
But, as you continue with your practice you find a much deeper effect happening - You become more aware of your internal energy and start to feel any blockages or problems with your body. I know several people who have realised they have something wrong and got medical attention quickly. Yes, medical attention is sometimes needed and when used along with chi kung practice a quick recovery is often possible. Obviously, this isn't always the case - sometimes your time is up!!!
Beyond this stage you find a more spiritual meaning behind your practice and you find yourself living much more in the flow of things (the Tao) - intuition often improves and you feel that harmony between mind, body and spirit often referred to as the 'three treasures' - Jing, Chi and Shen.
So don't just settle for the obvious benefits that come from practice - never stop searching and looking for the deeper mysteries that lie within Chi Kung.