here a little found from the German Wuhun-Magazin, which is a translated copy from the Chinese Wuhun Magazin.
I thought it might be an interesting quote (hope the english translation is not to bad) from one of the old masters.
From "What is Taijiquan"
no. 8, p44
How does one breath doing the exercises. The masters of Taijiquan of the old generations have no doubt about the four words: the breathing is natural.
Because the breathing is natural - not different as during dasily activites - there was at this times no need to explain it more detailed. But still some people expand the sentence "the breathing is natural" in an unatural way. Therefore Master Wu Jianquan feld the need to say the following:
"While eating or drinking nobody thinks about the breathing. I also never heard, that somebody got harmed by eating or drinking. Let us suggest, that while eating and drinking you also have to think when you have to breath in and out and how to use the qi. Then it would be unavoidable become harmed. That is the easiest way to explain it."