I would say that the POH or engine manual should have the last word on this.
In my case I can say that our Diamond Katana DV20 has had a technical directive from Swedish CAA to not turn the prop backwards, du to air bubbles forming in the oil pump.
The Super Cub manual on the other hand states that if engine start can't be accomplished due to flooding, the engine should be rotated so and so blades backwards to clear up fuel.
Hand propping is done on all our club aircraft at the start of the day, to insure compression is available on all cylinders, and also to "get the oil going" in cold weather conditions.