The ATR is fitted with PW120 series engines, and I have heard this comment many times.
This is either pure invention, or some procedure carried from another PW engine that is totally unrelated.
There is (was) no such thing in the ATR manuals.
Follow the manufacturer's manuals. If it was causing any damage, they would have included this procedure. It may well be on the PT6, but not on the PW120 series, at least not the ones mounted on ATR aircraft.