The vocal cords are widely open during whisper, which means; 1. There will be no contraction due to stress. 2. There will be no choking of air due to large flow area. 3. The exhale starts easily, which caueses relaxation. You can also have these effects, if you start speaking after you exhale for 2 seconds, depending on your exhale rate. By the way, airflow is not a speech technique. It just make sure that you avoid blocking at the beginning. After you start sentence without block, you should speak with a very clear pronounciation by opening the jaw to let the air out.