There are various kinds of breathing methods. In Japanese, "breathing method" is called "Kokyuho". Kokyu means breath and Ho means method. There are loads of Kokyuho schools and Dojos (Dojo means kind of "martial art school", and normally is used for the place to practice Japanese traditional martial arts: e.g. Karate Dojo) in Japan. And there are loads of Yoga or meditation or something like breathing-method-related groups or organizations or schools or activities or programs around the world. And, each one of them has its own style of breathing techniques.
No matter what it is, nor how it is called, after all it is about deep breathing: The act of breathing deep into one's lungs.
Having said that, breathing too deeply, like inhaling until you feel sick or exhaling until you feel you can exhale no more, will not give you a chance to master Ki energy but will ruin your health. If worst comes to worst, it may damage your lungs. And holding your breath too long may damage your brain.
Inhaling 80 percent and exhaling 80 are deep enough.
But, if you are those who says;
"That's not enough! Too easy! It has to be an ascetic practice! You have to inhale the air until it breaks your lungs and you have to exhale it until you faint dead away!"
If you think so, I don't stop you so go ahead.
Ok now, what happens when you inhale?
Yes that's right.
We inhale oxygen while we are taking breaths.
Then, mitochondria, the energy factories of the cells, produce energy. With this energy, animals including human can move and walk and run and do this and do that happily ever after.
As long as you are healthy, you can survive without eating one to two weeks. But even if you are perfectly healthy, if you hold your breath ten minutes and you may faint dead away, or worst comes to worst, you might even die.
We have to keep breathing all the time. Even when you feel too lazy to breath, you cannot stop it; nevertheless, if you get too much oxygen, the oxygen becomes a poisonous substance which produces active oxygen.
Whatever you do, better do it moderately.
The effect of doing something too much tends to be contrary to what was expected. The things sometimes may go worse than "Too much of something is like something that's not enough.".
Even if there is a super excellent breathing method, doing it all day long without any break is just ridiculous.
Breathing exercise may be good for your health. But if you do it too much, not only active oxygen which is the cause of the various diseases will be overproduced, but also the amount of oxygen your body take in will become smaller. Because when too much oxygen keeps coming in all the time, your body will try to control the amount of oxygen in your body; it is just opposite to high altitude (low-oxygen) training to get effect on marathon race, which improves oxygen intake. Oxygen intake capacity will be decreased if you get too much oxygen.