When we are beginning yoga students and just starting to learn the basic yoga poses, our understanding is understandably superficial for some time. We learn where to put our body parts -- our arms, legs, head and trunk. We learn the basic techniques of straightening and stretching our arms and legs, and of lifting and opening the chest. We learn basic key elements of movement and alignment. We paint the "picture" of our beginning poses with broad strokes.
As we practice these basic poses over time, we become stronger, more flexible and stable, and more aware of how our body works, which readies us for more difficult poses.
When we become more experienced, we add refinement to the poses. We're given extra detail in the instructions to fine-tune our alignment and to strengthen our level of concentration. We learn to pay attention to the finer details while still maintaining the whole of the pose with integrity. This brings our minds to a state of inner steadiness.
It makes no sense to add these "refinements" too early in our practice and learning.
Compare the videos below --
Senior Iyengar Yoga teacher, John Schumacher gives good, clear instructions and demonstration for Utthita trikonasana -- Extended triangle pose. This set of basic instructions is good for beginners and for more seasoned students. (Note that he is "mirroring" the instructions. So if you are following his instructions, he is your mirror, i.e. while he tells you to turn your right leg out, he is turning his left leg out.)
John Schumacher has a series of these YouTube videos for a number of the basic yoga poses, and they're all clearly presented. Anyone who is a serious yoga student or yoga teacher would benefit from watching these videos.
Contrast the previous video with the following video of Senior Iyengar Yoga teacher, Lois Steinberg, teaching Utthita trikonasana to a group of experienced students (in Poland). These students have proficiency in the basics and are being taught some rather intriguing details that would not be helpful or appropriate for beginners. For seasoned students, though, this type of work deepens their understanding of the pose.
Any pose becomes endlessly fascinating as we learn to work more deeply in the pose.