The beautiful thing about yoga is that it can both relax you or kick your ass, and sometimes do both during the same session.
Any movement is good movement, and yoga can strengthen your body, albeit in a different way from weightlifting. You create resistance by using harder and harder variants of poses/movements, a bit like calisthenics or other bodyweight training.
Personally I try to get a yoga session (with a focus on balance and stretching) per week, on top of my strength/mobility workouts.