In Traditional Chinese Medicine (TCM), Mang Xiao belongs to the 'Purgative herbs that drain downward' category. The herbs in this category are those whose main purpose is to treat constipation. The fact they're 'purgative' means that they do so by removing Excess Heat in the Intestines and/or Stomach. As such all herbs in this category are Cold in nature, in order to cool the Heat.
Furthermore Mang Xiao is Cold in nature. This means that Mang Xiao 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 Mang Xiao can help restore a harmonious balance between Yin and Yang.
Mang Xiao also tastes Bitter and Salty. 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 Mang Xiao 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 Salty ingredients tend to have a draining effect in the body because they clear accumulations, remove Phlegm and soften hard lumps.
The tastes of ingredients in TCM also determine what Organs and Meridians they target. As such Mang Xiao is thought to target the Stomach and the Large intestine. In TCM the Stomach 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 Large Intestine on the other hand receives the "impure" parts of the digested food from the Small Intestine, absorbs the remaining fluids and excrete the remainder as feces.