For many people, practicing yoga is a means of removing the limitations that they feel, whether they are physical or mental. Understanding and gently pushing or changing the boundaries of the body will increase the practitioner's sense of what's possible.
The act of meditating and moving the body into different asanas while controling the breath is a way of exploring the universe and feeling a part of it. This opens up the practitioner's mind to the idea that they are not restricted to the physical body and the boundaries represented by it.
Advanced yogis often go on to contemplate the inner Self and its relation to the universe. With this practice comes a greater sense of boundlessness and inner peace.