Several years ago, I asked one of my classes what they would like to focus on that day and a woman piped up, "I don't come to yoga to think, I want you to think for me!" I found this statement disconcerting for a variety of reasons, the first of which it conjured up an image of mannequins set before me ready to be posed.
Granted, you shouldn't go to yoga class and proceed to plan your day or worry about what's in your inbox at work. However, you should be present during class and focused on your body and breath in the poses. I want my students to ask themselves, "Can I go deeper or should I back out? How is my breathing? Is it rapid and labored or slow and easy?"
I also want my students to learn to "pose" themselves. In other words, learn what the correct alignment feels like and to adjust as needed. I'm there as a reminder and to help make adjustments but like I'm always saying, "I'm not in your body." I don't know how the pose feels to you. I can tell you how it looks but I don't know if it's hurting somewhere and needs to be modified.
When I teach a class I want to teach, not lead. However, most of us are used to listening with our eyes and not with our ears. This is evident by the number of people who make the same gestures I make when I'm talking with my hands during a pose. Or when I go to move a piece of hair from my eye several hands invariably move toward faces until their owners realize what's really happening.
Likewise, how many times have you been alone at home and heard a noise downstairs and began looking around the room? I do it too. Obviously, the noise isn't in the room but the instinct is to look and not listen.
In yoga class it's imperative that students listen with their ears because yoga poses have many nuances. Most have to be explained verbally. When you merely mimic the teacher you miss out on many of the pose's benefits. It's hard to ever reach the deeper levels of a pose or begin to understand the purpose of the pose by just following along. With just the feet alone, there are several minor adjustments that can change the whole dynamic of the pose. A simple turn of the toes in triangle can deepen the stretch or take the pressure off the hamstrings.
So yes, yoga requires a lot of thought, but it does turn your focus away from your hectic day and allow you to do something good for both your mind and your body.