In fixed-wing, the horizontal tailplane is producing a downforce, because the centre of lift on the main wing is aft of the cg and tries to push the nose down. The tailplane balances that force. A rearward cg would allow the tailplane to present less downward force and less drag, extending the range.
In helicopters, some of the newer, bigger birds have tail rotors angled upwards to provide some lift and to extend the cg range, instead of having all the lift coming from a single point. In seeming opposition to this, the synch elevator produces a downward force, but mainly in an attempt to keep the fuselage more level. This has 2 advantages - it makes the cabin more comfortable for the pax, and it helps to minimise the drag from presenting the roof of the aircraft to the airflow. There is a bit of a battle between the upwards tail rotor and the movable elevator, but luckily the bigger machines have a computer to sort it out, not just a mechanical linkage like an old Huey.