This stance, also called a Reverse Cat Stance, is related to the Neko Ashi Dachi, but has the foot with little pressure moved slightly behind the other foot, rather than placed in front of it. The rear foot does not slide behind the other foot, but rather is simply moved backward from a natural stance position until it is located somewhere behind the ankle of the front foot. The amount the front foot moves back is application and situation dependent and is determined entirely by what you wish to accomplish.
The stance is often used to allow you to move your torso back or forward slightly while not relinquishing any ground, perhaps to avoid an incoming strike.
This stance is always transitional. It is adopted momentarily on the way to some other stance, strike, kick, or other subsequent action. It is commonly used as a way of feigning retreat and then subsequently charging forward with a counter attack. It is also used as a contemplative movement. It might be used when you are not entirely sure how to proceed next but by shifting into this stance you may suddenly see an opening that you can subsequently exploit. Keep in mind that this would all occur very quickly. One would not shift into this stance and then spend a few moments in deep contemplation while your opponent rains blows all over your body. Always be prepared to move into and out of this stance quickly.