In Traditional Chinese Medicine (TCM), Bai He belongs to the 'Tonic herbs for Yin Deficiency' category. Tonic herbs are used for patterns of Deficiency, when one lacks one of the 'Four Treasures' (Qi, Blood, Yin and Yang). Yin tonics have a heavy, moist nature. They either nourish the Kidneys and Liver or moisten the Lungs and Stomach. Extreme Yin Deficiency often translates into a 'burn-out', unfortunately more and more common among people today. It is worth mentioning that another great remedy against Yin Deficiency is a lot of rest and sleep; no herb will ever be able to replace this!
Furthermore Bai He is Cold in nature. This means that Bai He typically helps people who have too much 'Heat' in their body. 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 Bai He can help restore a harmonious balance between Yin and Yang.
Bai He also tastes Sweet. 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. Sweet ingredients like Bai He tends to slow down acute reactions and detoxify the body. They also have a tonic effect because they replenish Qi and Blood.
The tastes of ingredients in TCM also determine what Organs and Meridians they target. As such Bai He is thought to target the Heart and the Lung. In addition to regulating Blood flow, in TCM the Heart is believed to be the store of the 'Mind' which basically refers to someone's vitality. In addition to performing respiration, the Lungs are thought in TCM to be a key part of the production chain for Qi and the Body Fluids that nourish the body.