Ya true there is no harm in using props ,If you have some form of disability or physical problems.Otherwise one must do it without using props.
BKS iyengar is also teaching Yoga and making use of some specially made chairs.It is for their what they called "Mediacal batch" to treat the physical problems.( As i am just 300 mts away from his house in modern colony Pune area , i know it better)
