Some confusing information given earlier.
Both SAS and ATT require force trim to be on to work. If force trim is off, the SAS actuators will move the cockpit controls instead of the rotor head.
SAS typically will only damp out rates.
Force trim can be used to re-datum the attitude being held. But holding the force trim button down disables attitude hold.
If the stick is moved with the force trim engaged (and the force trim button is not held down), the helicopter will move, but return to the datum when the stick is returned to the original position (i.e. the forces on the stick are released).
If anyone wants a document on how to demonstrate the various modes to gain a better understanding of how these systems work, please pm me.