Most likely you often find yourself like this: sitting, shoulders slumped, back muscles lengthened and hip flexors (the front of your hip) engaged bringing thighs closer to torso. This tightens your chest muscles, weakens your back muscles, and also tightens your hips and hamstrings (the back of your thigh).
Physically, yoga gives you the opportunity to counter this habitual position of sitting (at your desk, in the car, on the bus, on the couch, at the dinner table, etc.). Yoga can bring strength to the muscles of your back body, open and stretch the chest, lengthen the hip (flexors), and stretch and strengthen your hamstrings. When practiced regularly you gainbetter posture, less stress is put on your internal organs, and you feel taller, more confident and energetic.
Spiritually, the traditional aim and meaning of yoga is union or balance. In addition to helping physically, yoga allows your body and mind to become quiet, still and peaceful. After moving the body with the breath for any extended amount of time it is much easier to find this quiet, still and peaceful place in your body and mind. When we give the breath a chance to be the leader instead of our monkey mind we hand over the reigns to Spirit. Read the published scholarly paper I helped author here.