I think I may (or may not...) understand what tatpurusa is saying.
I do agree that sometimes flexibility is an issue as well as other problems, but perhaps from the viewpoints of the traditional medical practices (ex. Tibetan medicine) a different perspective could be considered also. From these theories, in terms of the flow of energy (lung-Tib.) throughout the channels in the body, most of us have "blockages" or "knots" which can (and do) restrict the proper flow. Among other benefits such as overall health, a proper flow allows for more flexibility and less pain.
In a tantric context, without going into much detail, some of these "exercises" when combined with certain methods can have the effective purpose and results of helping to remove or clearing some of these "inner obstacles". Certainly not what they could appear to be. But the "inner" practices are an important aspect, and should be learned from a qualified teacher. Luckily in the last number of years, through great compassion in our degenerate age, some of these practices have been introduced to the general public whereas in the past they were fairly guarded. These practices can have a great effect and impact on both a healthy body and mind, and could also a serve as a precursor for more advanced practices. I have seen first hand, the results of these practices. And it improves sitting also!