I have wondered why we bother with 'flaps zero = in trail'; I have not been able to discern any significant difference in the way plane handles or speed whether flaps are in reflex = -3 deg or in trail = 0 deg. I understand the speed limit for the zero deg position because the flap is not retracted up against the rear spar. Why not use just three settings of -3 deg, 15 deg and 30 deg? Anyone have a good reason for using four positions, other than Vans suggests it?