For years I oscillated between doing traditional hatha yoga or graceful vinyasas. The former involves holding steady poses to get maximum benefit from them. Vinyasas, on the other hand, involve moving from one asana to another, making it a cardio activity on the physical level, thereby improving stamina as well as balance.
The grace of getting in and out of a posture comes with fluidity of movement. However, one doesn't have to do vinyasas to experience grace, and even hatha yoga can display beautiful fluidity. Confusing?
In order for a posture to unfold all of its benefits, I need to hold it steadily. For instance, if I am supposed to join my palms in the vrikshasana or keep my knees together in utktasana, I need to keep them together steadily! Being shaky in the knees, or not joining the palms together makes the entire posture a bit shaky. While there is no need to tense the body, scanning the body with awareness often ensures that the posture is steady, and hence, effective.
A yoga session needs to be balanced, whether one is part of a class or practicing on one's own. If, at the end of the session, your entire body is relaxed and refreshed, it shows that the session was balanced.
As exhilarating as I find the surya namaskar, even a seemingly simple yoga sequence can mobilise energy through my body. The deep and beautiful effects of yoga are experienced with this movement of energy (and removal of energy blocks) in my body. This is also why a consistent yoga practice is highly beneficial, because it keeps the energy moving and keeps removing blockages within the energy body.
While I have learnt over time to keep my neck and shoulders relaxed during asana practice, I need to remember subtle things like keeping my tongue, throat and jaw relaxed and soft. Ignoring seemingly unimportant instructions like these can also lead to big physiological problems. And conversely, following these expands and deepens one's awareness, and improves one's asana practice.
Just goes to prove the yoga may look deceptively simple, but with the complex interplay of various muscles, energy movement and mental awareness, yoga really works on body, mind and soul.