When teaching Yoga classes to the public, it is important to remember that what we see as useful may be worthless to new students who are entering Yoga. After Yoga certification a teacher may see that last four limbs of Patanjali's Yoga as important. These last four limbs of Yoga are very useful for self-realization, concentration, meditation, and Samadhi.
Some interns and Yoga teacher trainers believe the heart and soul of Yoga is asana practice. This may be so in some fitness oriented Hatha Yoga styles, but it isn't the case for all of Yoga. Many Yoga styles are designed for the maintenance of your mind on a spiritual, mental, and emotional level.