Well, this is a controversial topic, but for me I couldn't imagine smoking a pipe without clenching. Old school pipe smokers all clenched. You see this in old movies, and news clips from the era. Piping was a hands free operation. Men would pipe whilst typing, writing or reading. Hands free. Piping wasn't a "hobby" -it was a life style. Many men smoked from dawn to dusk and lived lives significantly longer than many do today.
Basically, after the first charing light and dicking around with the tamper a bit, the first and final light is lit. The pipe stays in the mouth more or less till it's done. To better grip the stem, and prevent chatter or tooth marks I use a bit protector. Not those big ugly rubber ones from China. Instead I cut my own thin rings out of surgical Tygon tubing. These little rings slide on the bit just behind the button, as your facing the opening. After piping and cleaning they slide off before the pipe is racked. Otherwise these things promote stem oxidation on vulcanite.
When you clench, your piping cadence develops naturally with your breath. You then sip for flavor. An added bonus is the pipe rarely goes out. Another bonus to clenching is that piping then becomes mindless, in the Zen sense of the word. And, for me, the less thought put into a smoke, why the more transcendent the smoke.
Yes indeedy, piping sure teaches a hell of a lot more than just how to smoke a pipe. I think clenching, snorking, and gently sipping to maintain a barely burning smoulder is key! And I'd venture a guess that clenchers have a far shorter learning curve than hand holders. And that's why I recommend it for beginners. When I see pipers billowing great clouds of smoke, like a locomotive, why I know their bowls are way too hot. And the gentle tobacco oils are being vaporized before the piper is able to taste them.
At least that how I see it.