Most schools of Qi Gong today sell themselves as being about health and healing. This is because mainly the people promoting those schools either have no real grounding in what Qi Gong is for, or are aware but felt obliged to keep the real purpose hidden. In China, Qi Gong was very badly persecuted during most of the Communist period. It was only allowed to be revived in the time after the terrible persecutions of the Maoist Cultural Revolution, when the Chinese Government eased away from attacking traditional Chinese culture, and when the nation was facing a health-infrastructure crisis.
In fact, there was no such term as "Qi Gong" before the modern age, this was a name created to unite concepts in traditional Chinese healing, cultivation practice, and internal martial arts. The government began to promote Qi Gong, not as a spiritual practice of cultivation, but as a system for improving health and wellness. So many opportunists who had little or no real understanding of cultivation set themselves up as "qi gong healers", while some of the genuine teachers began to teach again by hiding their more esoteric training behind the facade of "health and healing". In fact, this fit in nicely with the historical tradition of "secret schools", where serious Qi Gong masters would hide the nature of their teaching.
But regardless, Qi Gong was not meant to be about health, or healing. It was meant to be about cultivation for the purpose of eventual enlightenment.
So how useful is Qi Gong, for someone who is only interested in preserving their health or healing some kind of ailment?
Regarding health issues and Yi Fa Qi Gong; or health issues and Qi Gong in general, you have to consider the sources of various health problems. They are caused by one of a selection of sources:
0. Accidents or short-term illness: a broken leg or a cold or upset stomach are not really caused by anything in most cases, except misfortune. These problems do not really need Qi Gong to heal.
1. Genetics: This is one of the most common causes of non-acute health problems. Recent medical studies have found that a great number of health issues are largely caused by genetic predisposition. This is a product of birth. Qi Gong can't really do anything to prevent these problems. There's not really anything Qi Gong needs to do about these, in terms of prevention, and only limited amounts it can do in terms of treatment.
2. Environmental issues: These are health issues caused by where you are, by elements of your environment. This also includes things you might have a genetic predisposition toward, but would not be affected by it without being exposed to some environmental trigger. These health problems can sometimes be resolved by changing your environment. Doing Qi Gong without making changes in your environment won't be of any real help.
3. Lifestyle/choice issues: Some health problems are caused as a consequence of your lifestyle or behaviours, related to eating habits, sleeping habits, drinking, drugs, smoking, or other choices. Again, if you don't change your lifestyle, Qi Gong will not be of help here.
4. Stress or emotional issues: some health problems appear as consequences of mental stress or emotional tension manifesting in the body. The best resolution to these problems is through relaxation, meditation, and the expanding of your own consciousness until your attachments disentangle themselves. The exercises of Yi Fa Qi Gong are effective at dealing with these issues, if properly practiced.
So this is why I do not put very much emphasis on 'health' in Qi Gong practice. Anything related to health that can actually honestly be helped by Qi Gong can and will be helped by performing Yi Fa Qi Gong correctly, even though Yi Fa Qi Gong's primary goal is not health but Enlightenment.
None of the other sources of health problems can be significantly helped by any Qi Gong, even those forms of Qi Gong that allege to be about health.
