Yoga is a great practice for so many reasons. But just like strength training, you aren't likely to get much benefit if you aren't a good student of it, if you don't have a good instructor, or if you don't practice it well. By "practice it well" I mean things like, challenge yourself appropriately, pay attention to what's going on with your body, and adapt the amount of stress/recovery of whatever method or class you pick (challenging, restorative, etc.) to the rest of your training.
Some things I get out of it by doing it once or twice a week: A regular "soft practice" to balance strength training and cardio, breathing, balance, odd stretches that I would otherwise forget to do, a "check in" to see if there's anything weird going on with my mobility or movement, isometric strength work, bodyweight strength practice, time in contact with the ground in various poses, experiencing the tension/relaxation relationships in a vast variety of ways. I also learn a lot about movement from watching others in class... their restrictions, their challenges, their strengths and weaknesses. Yoga is supposed to be about yourself and not others, but I find it to be a great learning experience in this way.