FFF...yes I have checked the manuals and nothing in either regarding it.
There is another reason we do it occasionally in the wet season. When parked if there is very heavy rain (tropical) with a tailwind, it is possible for water to be blown up the exhaust into the engine with expensive consequences on the subsequent engine start.
Engine covers are SOP, but occasionally for whatever reason they are not placed on the a/c. As such, engineers have advised to turn the props backwards several turns during the preflight/daily to allow water to drain out the valves.
CS
Thanks for the above replies!