Hatha Yoga

In class today we did a few asanas from the Hatha Yoga Pradipika. According to these texts it is supposed to lead to spiritual evolution if it is practiced everyday for 12 years. Some of these postures were difficult and when they were described it was difficult to picture how they were supposed to be performed. I found it quite odd that this particular kind of yoga can bring certain powers and improper practice can lead to the misuse of these powers. Overall, I dont really know what to think about this type of yoga but Im sure if I look more into I could make some sense of it.