"Yoga is 99% practice and 1% theory" ~ Sri Pattabhi Jois
Q: "How often should I practice?"
A: Yoga is a disciplined daily practice. To feel the beneficial physical and mental results it requires our commitment to a daily practice. If we eat healthy only once or twice a week, but don't the other days of the week, we'll likely not feel the benefits of a healthy diet.
Similarly with any training - to mark progress, we must practice regularly.