Starting positions are a reference for change. In yoga a starting position may be a position where it is fairly easy to relax and feel the body. They may also be a position from which it is easy or obvious in how to move towards the end position. If the goal is a complex posture then good starting positions offer the possibility of moving towards the complex posture step by step so that complexity is built towards one component at a time.
They also offer the opportunity for setting up the foundation of the posture. With a stable or solid or good foundation it is then easy to focus on what we are trying to do within the pose. Moving from the start position to the goal position we don’t have to worry about stability, with a good foundation we can simply focus on what we are trying to do within the pose.
With a starting posture and an ending or goal posture we have a goal to work towards. We have something that we can do while we are “doing” the posture, we can move from the starting position to the end position, and if we get to the end position that can be a new starting position for where we want to go to next. We can then figure out what we need to do to get there.
Starting positions are not set in stone. However, we do need a starting position so that we can move on from there. Ideally, starting positions make it as easy as possible to move towards our ending position. With experience, we can modify our starting position so that it is easier or as easy as possible to get to our ending position. We may also find that with experience, we can use different starting positions and we can find the way to get from where we are (no matter what starting position we use) to where we want to get to.
Also, so that we can improve the way we move from the start to the end, we can practice, feeling ourselves while we do the movement. If we do the movements smoothly, and slowly, we can develop our ability to control our body within that particular range of motion as well as our ability to sense or feel our body. We can then correct mistakes in our movements, or make our movements better even as we do the movements, we can correct ourselves or fine tune ourselves in real time.
As well as making our movements smooth, (controlled) we can also focus on creating space in our body and relaxing (extraneous contraction) as much as possible.