Hi Kariev - I'm doing STS 6.5 month rotation, with 3 days cardio, and yoga every evening. I'm of an age where I need to really stretch to keep flexible!!! (I'm 44). Whilst STS is bulking my muscles, the yoga seems to lengthen them - I really like the long, lean shape it seems to give me. I've developed great core strength, without too much of a 6 pack, and I can do Chatarunga push ups, no problem! Also when I'm lifting, say for a plie squat, I can go much deeper into the move.
The major difference, however, is in my hips. I hadn't realised how much tension I carried there. Once that started easing I found cardio much easier (weird, I know). It's almost as though I've oiled my body to keep it running smoothly!!!
HTH
Justine