Good questions. All your questions could be answered yes. I go with what is called for at the time. If I want to focus on a specific area or system (bones, nervous system etc.) that works, or a singular issue, like a sore joint ,that works too. I tend to do about three inhales and exhales for a specific area or system, very slowly with focused intent. Globally is also good. If you have a specific blockage, it makes sense , to me, to focus in on it, especially if it is a serious blockage. I think that anything you don't want to hold can be released. I even will consider a bad habit as an energetic pattern that can be removed with this exercise. I am sure you will get other good feedback. I am not sure what you mean by preventively. If nothing is blocked, there is nothing there to clear, although the exercises as a whole prevent illness through daily practice. I don't think it is good to think of not getting a specific illness that you don't have , and focusing there. You wouldn't want to call that into conscious thought.
