Hanging meat is a traditional method used by butchers to improve the quality and taste of meat. It involves allowing the meat to rest for a period of time after it has been slaughtered, so that it can go through a process called aging.
During this time, enzymes in the meat break down the muscle tissue and connective tissue, making the meat more tender. Hanging the meat also allows any excess moisture to evaporate, which concentrates the flavor and creates a firmer texture.
Additionally, hanging the meat can help to enable the blood to congeal and facilitate jointing. It does not, however, increase leanness, as this is determined by the breed and diet of the animal.
In summary, hanging meat is not strictly necessary, but it can improve the quality and taste of the meat by making it more tender and flavorful.