I have always been a fitness buff since high school whether I do running, weights or other gym activities. Fitness has been an integral part of my life. It has allowed me to climb the tallest peaks in the Philippines, dive 18m on one breath, ride across a mountain range on a mountain bike, etc. The world simply opens up because you are fit.
Yoga has been the cornerstone of all these fitness activities. But yoga was never designed to be a comprehensive workout routine (it was designed for something much greater...a gateway into the divine). There are a few missing components in the asanas - cardio-vascular development, lats development (because you need a contraption to pull yourself up) and muscle-mass development. For these, I supplement my yoga program or integrate some components to provide a full body workout.
For yoga students with specific objectives, such as weight-loss, I would add a cardio-vascular component like a high intensity interval cardio or rope skipping. Even though my addition is not part of traditional yoga, I still view it as yoga for as long as you reach your safety limit, synchronizing breath with movement and being mentally focused on what is being done. Lastly, I add the intention into the gamut - it sets the direction.
A sound body gives you a sound mind, retards the ageing process and keeps the doctor away.