Qustion: Why are we expected to study philosophy of yoga as well as doing the practices? Surely philosophy will be a distraction and it would be better just to practice without bothering about the theoretical background?
Answer: Experience over the centuries has shown that those who do not study the traditional philosophy which gives the basis to their yoga practice, find it difficult to keep up the practice without having some philosophy behind it. So what often happens is, that they begin to develop their own philosophy. And because this new philosophy has no foundation in experience it is often self-defeating.
The advantage of the traditional philosophy is that it is clear and geared to meet the difficulties of the path as they have been mapped by many generations of yogis of the past. No-one can expect to be able to generate, in just a few years, a system of knowledge which has taken centuries to evolve.