Singers are often puzzled with two seemingly opposing concepts: letting the air out while at the same time conserving it. Equally puzzling can be this: you must keep the cords together; they must close for tone to be created. On the other hand air must come through for the cords to vibrate. There are differing pedagogical views of the application of these concepts. Others consider it paramount that there is good closure, even a tiny pinch of the glottis. Others think the air must flow and the cords will be closed through the Bernouilli effect.
All I can say is, both are right. Good closure will ensure clear tone, bad closure creates breathy tone. But even with good firm closure the air will come through in tiny puffs through the cords. So which should you think about; the closure or the air. This involves the whole body and the breathing apparatus obviously. And the final emphasis pedagogically speaking is always individual depending on the student. If the student has a breathy voice it will not be wise to stress airflow too much. If he/she has a tight, tense voice, the opposite is true. That´s why the same exercises will not do for everybody.
Airflow and air pressure are two different things. The old bel canto masters talked about lotta vocale, vocal competition – not meaning singing competition! – the pull between to opposing forces.
Excessive air pressure can hinder vocal fold vibration. The female middle range especially can be severely affected , the folds vibrating with too thick mass. Thick folds in the middle range require ever more pressure with unfavourable results: pitch problems and compensatory tensions. Male singers can usually cope with less problems because their vocal fold mass is always greater but they should learn to thin their folds, too, if they want to be able to sing high notes. That´s called technique!