The neutral position in a powered system, such as most of the Boeing aircraft types, uses a spring loaded Vee cam that would force the elevators to the neutral position should the pilot release the controls. Aerodynamic loads on the elevator cannot do this in a powered system. But what is the correct neutral position for a given stabilser position?
The Vee cam is mechanically repositioned according to a predetermined schedule dependent upon movement of the stabiliser, so that with no control input, the position adopted by the elevator relative to the stabiliser changes. The positioning schedule is set so that the elevator remains biased to the aerodynamic neutral applicable for whatever is the current position of the stabiliser. So mono, the neutral shift system eliminates the undesirable aerodynamic loads on the elevator and this aerodynamically neutral position is achieved by a mechanical system. Does that make it any clearer?
Then we could move onto the neutral shift sensing system that allows the autopilot to remain synchronised to the applicable neutral position while it is engaged. One wouldn't want to jump to a new neutral when disengaging the autopilot would one? Ah! Such are the complexities of the AFCS.
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Through difficulties to the cinema