Trikonasana opens the chest, shoulders and hips while elongating the spine (I even hear a soft click of the vertebrae aligning the spine in this asana). I can literally feel the asana moving my body into correct alignment. It improves flexibility and builds strength. It stretches and tones the muscles of the legs, abs and waist.
I always find that this asana immediately relieves stress, tension and anxiety. It alleviates anxiety and other symptoms of stress, including a racing heart and other symptoms of the sympathetic nervous system. Stressors in daily life can activate the sympathetic nervous system or the fight or flight response and counteracts this through activating the parasympathetic nervous system, reducing blood pressure, the heart rate and breathing rate. Blood flow is redirected to the digestive and reproductive organs, and the endocrine and lymphatic system. Through focusing on the breath in the asana, deep and smooth, cortisol (the stress hormone) is greatly reduced.
It is mentally rejuvenating. This asana is also good for digestion and elimination of food.