In Nihon Goshin Aikido we have 15 Ki techniques and we must be able to perform 10 for ShoDan. The reason we train in Ki is to develop Mushin (mind of no mind. in other words you must be centered and aware of your environment with out mentally focusing on any one thing.). Through our training we learn to control our mind and body even in adversity. That is the test. Assume two people are trying to lift you, and you remain calm and relaxed they will not be able to and while they are lifting the last part of the test is to do a front kick while keeping the other foot on the mat. If you are centered you will succeed and if your not centered up you go.
How does this help you in battle? Through thousands of repetitions of your techniques your body knows how to react. But your mind may hinder your natural ability to respond to attacks. By being centered you will see the attacks clearly and the body will respond accordingly.
Does any one else train in Ki techniques? Do you believe in Ki?