The word asana means posture. You find the ending of every posture in Sanskrit to end with this word. So adho mukha svanasana is the posture of the downward-facing dog.
The original yogic teachings intended for postures to be comfortable ways to hold a position for an extended period of time for the purposes of meditation. Only a few basic poses were originally prescribed.
The evolution of the hundreds of postures prescribed by various lineages of yoga is perhaps based on the desire to bring a sense of healthfulness and fitness to the body. The idea that a healthy body helps bring focus to the mind is at the essence of the yogic movement today.
It can also be argued that the obsession with asana over any other aspect of a yoga practice is contrary to the intention of the yogic goal of a blissful, meditative state. In fact, a vinyasa or flow-based yoga seems to contradict Patanjili’s notion of using posture to achieve stillness. At the same time, however, we may also argue that vinyasa-based yoga may be a viable part of any practice that leads to a mindful or meditative state!
It is the aim of Hatha Slow Yoga to find a balance. Taking three to ten breaths in every asana provides ample time to find a state of mindfulness. And when practicing on your own, take as long as possible in finding comfort in each asana. In addition, it is encouraged to take a single posture during every session to practice at least 15-20 minutes of meditation wherever you are on the meditative path to bliss.