Mitty,

So (1) is everyone taught to do it on final? (2) Why? (3) What's wrong with
doing it on downwind?


Yes, noise, noise. Just listen to a Bonanza turning on the chain saw on
downwind once, and you'll never again say it's only a "small noise increase".
The effect, while differing from type to type, is huge. If you want airports
to stay open, don't do it on downwind.

Also, in case of a go-around, it is probably anyway a good idea to think in
terms of "all levers go full forward" rather than just "throttle full
forward".

--
Thomas Borchert (EDDH)