Short and taut vs Long and Loose :
The Two ways of performing Asanas
Those who have tried various schools of yoga, would know that there are two ways people perform the king of all poses, Shirashasana - one way is short and taut and the other is long and loose. The former method is characteristic of the Ashtanga Vinyasa school which strictly follows the principles of Hatha Yoga, where people hold the pose in a taut fashion with all the bandhas engaged and the toes pointed and without any slackness of the body. The latter method is followed in Iyengar and Yin Yoga schools. In this method of doing Shirashasana, people hold the pose for a long time and relax the body. Renowned yoga experts like Dr. H.R. Nagendra, the yoga adviser for the prime minister of India and a expert on the therapeutic effects of yoga, generally classify asana practice into two lineages or schools - the Hatha Yoga school and the Patanjala Yoga school. Patanjali's definition of asana in the Yoga Sutras is "Sthira Sukham Asanam", which means "Steadiness and Comfort characterize a yoga posture". Patanjali also says that when one relaxes after entering a pose one can maintain the pose for a long time blissfully. This is given in the sutra, "Prayatna Shaitilya Anantha Samapattibhyam".
On the other hand, Gheranda Samhita (see figure below), a hatha yoga text, uses the words "fire" and "bake the body" to characterize yoga. The word "Hatha" itself means "force". Hence hatha yoga schools such as the Ashtanga Vinyasa school are characterized by dynamic exercises that use a lot of mudras and bandhas to raise the kundaline. See this video by Dr. H.R. Nagendra on the Hatha Yoga Pradipika at 14:12.
While both ancient schools of asana practice are meant to steady the mind, one through energetic means to enter calm states (just like the eye of a storm), and the other through progressive relaxation, which schools suits one highly depends on the individual nature and age of the person.