I used to fly for my biennial with a really good instructor in the Chippy - mostly we'd do aeros. But he also had a 'thing' about not lowering flaps in the turn.
Now I like to keep it tight in the circuit, so flaps go down (at least 2nd stage do) in the final turn and I also re-trim in the turn (I know the aeroplane very well so this isn't a problem and I can feel when the trim is right for the turn) before rolling out on short final. The Chipmunk can, as you may know, suffer asymmetric flap as each is individually actuated by a cable - which can snap. So he had a point. But I don't think that would be more of a problem for the experienced pilot than it happening in S&L flight.
But I think it was really a hangover from of his instructional flying with ab initio studes, which was his daily bread and butter.