[jacquesm]

In a plane (where you are minimizing drag when an engine is out) you would put the blades such that the prop presents the minimum surface to the airstream, in a windmill you have a choice, you can put the blade in 'neutral' by picking one of two 90 degree offset orientations, one parallel to the apparent wind, one perpendicular to it. In either case the blades won't turn.

For safety purposes 'coarse' is not always the best position because if the wind is heavy enough it will have a lot of torque to work with, 'flat' is much easier to hold down with a brake.