I recently noted an interesting online article from Frøydis Ree Wekre on the rules of horn playing. Basically she says in “Never Say Never – Again” to never say never and to actually try doing things people say to never do. She gives this great example.
“Never puff your cheeks.” My first horn teacher told me this, and I followed his advice obediently. However, one evening, as I was watching the orchestra where he played, I noticed something strange in the horn section; surprisingly for me, my own teacher puffed his cheeks occasionally! When asked about this during my next lesson, he thought about it for a while, then smiled and held firm to his earlier advice, but of course, the grain of doubt had been put into my mind. Later I have found that puffing the cheeks occasionally when playing in certain ranges or dynamics might help to give stiff corner muscles a quick, temporary relaxation. It might also help producing a different tone colour, if one is unable to create that on the normal, non-puffed setting. So, my answer to this rule would be: Yes, for the most part, although no rule without exceptions!
Read the whole article, she makes some really important points, especially about tonguing. This article was written about ten years ago and was originally published in The Horn Call; the posted version in the IHS website does not give publication details.
There is one other article posted in the IHS site by Wekre. In this article she actually sets up a bit of a rule of her own. She does not say to never use the triple horn but she does rather discourage it. Check out what she says on this, and then I say try one out for yourself; find out what all the buzz is about. It is not for everyone but in an American orchestral context it is a great option for the high horn player.