"We hear of great sages who obtain the mastery of nature by thapas, they reduce the emelmental forces to their control". "Man can participate in divine power by hidden (secret) force of magic". This was the common sense in Vedic India. The practitioners of witchcraft were (and still) readily accepted. We find people sitting in the midst of five fires, standing on one leg, holding an arm above the head, all for the purpose of commanding the forces of nature and subduing the gods to their will (this is a genuine sarcasm of an India philosopher).
The only value of Yoga practices is to gain the fine control over the mind through the breathing techniques, and thus to attain the Unity with the Whole which is possible only for a [100% idle] unaggitated mind.
All these "higher yogas", such as Karma Yoga and other "secret teachings" of numerous lesser sects of Hinduism (from which these "teachings" have been incorporated without understanding into Tibetan tradition in the age of bulk translations) are, well, means to support sectarian Ponzy schemes and even commercialization of naive folklore. There are thousands of web-pages about these "yogas" elsewhere.
Have you seen those stoned fat "yogis" on Kumbh Mela? Do you really believe that this is how a balanced, austere, well-trained, healthy body looks like? Come on!
What is Yoga "really"
In short, it is a basic set of principles, discovered by ancient Hindu ascetics and since then evolved into a philosophy of well-being. The key principle, in ancient wording, was the circulation of Prana - a "vital cosmic energy" through the body and mind. In modern understanding this would be the notion of the balance we call Homeostasis which a body (all its major sub-systems) and non-verbal mind together are trying to maintain unceasingly. The ability of extracting Prana from the air, water and food, the yogic ability to control Prana and even to direct it to the various organs of the body is what we would call a natural habits, which help to maintain Homeostasis - the subtle balance of proper ventilation, circulation, nutrition, physical exercises and hence proper states of the mind.
In other words, Yoga in a philosophy of not breaking the intentions of the Nature which made us as best as it could be, to stick to the "natural habits" (physical and mental!) of breathing, chewing, drinking, eating, standing, sitting, etc. and avoiding the new, which are unnatural, unhealthy and quickly break the subtle balance.
The emphasis on breathing techniques is not an incident or mere fanciness. The lungs are considered by yogis as a great crematorium, which purifies entire body. This is, of course, a correct intuition about the immense importance of breathing as not mere a process of oxygen intake, but the way of getting rid of carbon dioxide and other by-product in the first place, and its role in the maintenance of proper pH and temperature of the whole body. There is a reason of why we cannot stop breathing even for a couple of minutes.
But the breathing and postures (asanas) are not even close to the whole thing. It includes every aspect of human existence, the breath comes first because it is most important, circulation (this is what all the asanas are all about) comes next, but there are also nutrition and the whole "higher" philosophy of proper understanding of physical and mental phenomena and especially its source (Brahman), of having a proper mental attitudes (about being one and the same with Brahman, so immortal and indestructible - ethernal) and states of the mind.
If today we substitute the word Brahman to the word "Universe" (of which we all are mere products) almost every intution of Yoga philosophy (expressed in poetical wording) would still hold.