"This mode may not be ideal to use when wanting to drive in a sedate manner; nor when road conditions are very slippery, due to ice, snow or torrential rain – because loss of tire traction may be experienced (wheel spin during acceleration, and may also result in road wheel locking during downshifts at high engine rpms under closed throttle).
On 4motion or quattro-equipped vehicles this may be partially offset by the drivetrain maintaining full-time engagement of the rear differential in S mode, so power distribution under loss of front-wheel traction may be marginally improved."
I didn't quickly find other references to S locking the Haldex or if this holds true in T6, definitely something to test one of these days!