O'Beefer (not one of my old beefers I hope...)
As far as I know it's to help out with tail rotor roll in forward flight.(amongst other things)
AS350 tail rotor roll gives right wing low, so as the horizontal stab gives a nose up pitch via lift acting 'downwards' in flight, then if the port side of horizontal stab gives more lift 'downwards' therefore opposite rolling moment to tail rotor roll!
Alternatively it could be there to stop tools rolling off!
