Parsvottanasana is a pose that teaches one to facilitate freedom by setting up boundaries.
Patanjali´s eighth "limb" of yoga is samadhi, an ultimate experience of yogic freedom. In order to reach it, one must first practice the other seven limbs that precede it. The first one, yama, is a group of ethical principles that shall be followed. These principles are setting up boundaries that then later lead to the the ultimate freedom - samadhi. Similarly, in parsvottanasana, setting a firm foundation with alignment teaches one to cultivate a sense of freedom. The boundaries and structure of alignment and muscular action that one establishes through this sequence allows for a safe and deep release as well as the ability to experience more freedom of movement in this and other poses.