In Traditional Chinese Medicine (TCM), Qin Jiao belongs to the 'Herbs that dispel Wind and Dampness' category. These herbs typically help treat what's called 'bi pain' (i.e. painful obstruction) in TCM. This roughly corresponds to arthritic and rheumatic conditions with pain, stiffness and numbness of the bones, joints and muscles.
Furthermore Qin Jiao is Cool in nature. This means that Qin Jiao tends to help people who have too much 'Heat' in their body, although with less effect than a plant that would be Cold in nature. Balance between Yin and Yang is a key health concept in TCM. Those who have too much Heat in their body are said to either have a Yang Excess (because Yang is Hot in nature) or a Yin deficiency (Yin is Cold in Nature). Depending on your condition Qin Jiao can help restore a harmonious balance between Yin and Yang.
Qin Jiao also tastes Bitter and Pungent. The so-called 'Five Phases' theory in Chinese Medicine states that the taste of TCM ingredients is a key determinant of their action in the body. Bitter ingredients like Qin Jiao tends to have a cleansing action on the body by clearing Heat, drying Dampness and promoting elimination via urination or bowel movements. On the other hand Pungent ingredients tend to promote the circulations of Qi and Body Fluids. That's why for instance someone tends to sweat a lot when they eat spicy/pungent food.
The tastes of ingredients in TCM also determine what Organs and Meridians they target. As such Qin Jiao is thought to target the Gallbladder, the Stomach and the Liver. Similar to modern medicine, in TCM the Gallbladder stores and releases bile produced by the Liver. It also controls the emotion of decisiveness. The Stomach on the other hand is responsible for receiving and ripening ingested food and fluids. It is also tasked with descending the digested elements downwards to the Small Intestine. The Liver is often referred as the body's "general" because it is in charge of regulating the movements of Qi and the Body Fluids. It also takes a leading role in balancing our emotions.