On one level, it’s about becoming more flexible and more able to do the poses.
On another level, it’s about increasing body awareness. With time and practice, you get so you can pay attention to subtle changes in your body, and to exactly the teeny shift in, say, your right calf muscle, that puts you into a “better” version of the pose. A friend likened it to being able to make repairs on your car while driving 80 miles an hour down the highway.
On another level, it’s about paying attention in general, observing what is happening right now.
I remember the first time I realized that in Savasana (corpse pose) we are all, every single human being, breathing the same breath. Yoga helps me arrive at that.