My thought process was that the SAS works on providing a opposite force to a roll / pitch rate induced due to wind or (pitch and roll on deck) to try and minimise disc movement caused due to this external stimulus. The ATT mode on the other hand holds the disc attitude in position
Well, that's weird, the S76 and B412s I have flown used SAS just to smooth out the hand flying (no attitude hold or any kind of other autopilot function) and no Force Trim on, and in ATT mode, (force trim must be on) it held the last attitude you had when you took your finger/thumb off the force trim release button.
On a ship deck, force trim was OFF and the stick just held, because the autopilot might make some strange inputs to counteract pitch/roll.
In a Huey, force trim just held the stick in position, which meant that if you went hands-free, you would eventually roll up in a ball.