Here's a little anatomy quiz for you. The hip adductors are responsible for which of the following common yoga issues: (1) You have difficulty holding your legs together in inversions; (2) Your knees pop up in sitting poses like Baddha Konasana (Bound Angle Pose); (3) Your legs slip down your arms in arm balances like Bakasana (Crane Pose); (4) Your legs won't separate very far in Upavistha Konasana (Wide-Angle Seated Forward Bend).
Answer: All of the above. The hip adductors are a group of five muscles that occupy your inner thighs between the quadriceps on the front of the leg and the hamstrings on the back. When these muscles contract, they help draw your thighs together in poses like inversions and arm balances; when they stretch, they open up poses like Baddha Konasana and Upavistha Kona-sana. Whether stretching or contracting, they're crucial in a wide variety of poses. Strengthening and stretching the inner-leg muscles will improve the aforementioned poses, and you'll be able to sit on the floor with greater ease—to play with children or pets, perhaps—and have both greater stability and an increased sense of freedom in your walking gait.