What we need to understand is that emotions are guidance to achieve our true desires, nothing more and nothing less. When you feel good, you are following your guidance, when you feel bad, you are not. The problem is that most people perceive emotions as unchangeable facts. And since we don't question facts we don't inquire about their purpose.
This practice can be used at moments of anxiety, fear, worry, or whatever is keeping our mind and emotions from being at peace. The main idea behind this practice is to return to the present, to self at times when we have an extremely emotional or mental experience. The purpose of this practice is to awaken from the experience that we are having, just like we wake up from a bad dream.