Why do you think it is a key? For me observing and playing with breath is just a way to overload brain with sensory/awareness activities so it can't keep the constant internal self chatter.
Just like walking a little slower than your normal pace and keeping your mind busy with that task.
Or like trying to count as many snowflakes as you can. Or when trying talk with people trying to be aware of you instinctive reactions and chose different reactions.
Talking here in the context of meditation and mind exercise. I am big fan of all kind breathing techniques.