Before we move on to analyze Hui Ming Jing (for practice purpose this text is more important), let us look at a summary of the theory as viewed from Taoist perspective (needless to say my own interpretation only). Similar theory appeared in both texts. My view is that one does not necessarily have to "buy into" this theory before one can get benefits from this practice, I mean for the modern man who looks for physical and mental health, with an option open to himself to develop his spirituality or religious belief as defined by birth or through free choice. With this in mind, I shall proceed with the theory.
Before one is born, chi is transmitted from the mother to the embryo who undergoes internal chi-breathing rather than external breathing. Once a baby is born, external breathing begins and there is a split of the self into consciousness (識神/魄) which stays at one's heart, and unconscious (元神/魂) which stays at between one's eye-brows. When a person is awake, he is being controlled by consciousness and attached to all kinds of pain and joyful events that shorten his life. When a person is asleep, his unconscious rules and he can travel to far away places in seconds. When one dies, his unconscious will leave his body and being dispersed (or reincarnate into different being as different Taoists have different belief systems). One way of salvation is that Taoist mediation or yoga can energize the unconscious so that it join itself with consciousness, the higher consciousness thus created is the self that can leave the body during meditative practice (out-of-body experience) and can also be immortal upon the depth of the person.
The practical benefit is that in order that the unconscious can be energized, firstly the mind must be controlled to a significant degree of calmness (resulting, for one thing, in a high EQ, besides the fact that a more relaxed body and mind is conducive to good physical and mental health), and secondly the body itself must be well balanced (good alignment and with blockages cleared) and full body well tuned (like，for example, "muscle as one" (肌肉如一).
The most important practical point is that this kind of practice (together with practices like tai-chi chi-kung) are most useful for people at middle-aged and above and people recovering from serious illness. For these people, exercises like jogging or swimming could not be a choice, and even if, they can no longer be as balanced and as effective.