The main structural alignment principles of mountain pose carry over to every standing position and most inversions and arm balances. Once the balance is created in the posture and found in other poses, stability is created in the asanas. This is a great introduction pose for beginners and will help the more seasoned practitioners find their center, use their legs and staying open and stable in their shoulders will help effortlessly support the body in inversions and arm balances.
Tadasana or mountain pose lays the ground work for understanding how to find effort and ease (In Chapter 2, sutra 46 Patanjali states: Sthira-Sukham Asanam) in your yoga practice. If you can find this balance simply standing it will carry through in all poses as your practice progresses.