we generally do not practice with kiai, which I initially found bizzaro coming from a karate background.
However, sensei has very interesting things to say concerning kiai. While demonstrating some sword techniques, (uke strikes shomenuchi, nage in hasso responds with shomenuchi right down uke's center, start of of kata 1)Sensei was nage, and did kiai when striking to uke's head with the sword. He explained that for the technique to work, his ki had to be clean and pure and that it is reflected in his kiai. If the kiai was clear and not ragged or throaty the ki was on.
Very cool and interesting...