When I was a kid all my teachers told me not to puff out my cheeks when playing, and to keep a calm/relaxed/unmoving facial expression at all times.  I learned over time, especially from Frøydis Ree Werke that keeping extra air in the cheeks for certain types of playing (low range, for example) can be advantageous.  I no longer think of it as fault in any player, and haven't done so for years.  In the middle-low range I have often used this technique to help get a richer, fuller sound.

But.......Saturday I discovered something that I hadn't been aware of at all.  Over the years, probably 15 or more, I have been playing with what can only be described as "chipmunk cheeks."  I am not talking about huge puffed out cheeks, but just small pockets of air just below the corners of the mouth.  I found this out because of the swelling and stitches from my widsom tooth extraction.  It was painful to play "normally" because of this "chipmunk" tendancy.  In the mirror I never saw the slight puffing in my facial expression which probably means that I have been doing it for so long that it seemed normal.

In order to play without pain I was obligated to control the minor puffing and hold the muscles and position in what could only be described as a text-book horn embouchure. (playing position, not mouthpiece)  No teacher has ever changed my embouchure because I have always had a really good position, but over the years as a professional I had apparently developed this habit sub-conciously.  As a professional you find solutions to performance issues that are often not text-book because you just have to get the job done (especially in contemporary music), but these need to be managed with care.  I, apparently, haven't been doing a good job with that.

It is amazing what you learn under the strangest circumstances.