The aerodynamic counterbalances are quite useful on aerobatic models .
On some ARFS they are simply styling effects.
On my 1/3 and large scale - I use them on the ailerons ends-for adding counterweight ( Igo for 25% cg on the aileron- .
On the rudder they really do unload the servos better - -on some designs - they are too effective and unless a lot of rudder holding power is used - they will cause tail wag as they self servo. seen it , fixed it, etc.
In some cases - a flat dam, attached to the rudder trailing edge is needed to act as a drogue - to keep the rudder from self servoing easily. This is a case of toooo much aero counterbalance area.
On elevators - on my tiny flat foam models -they also reduce elevator load - the servos are tiny and a simple flat hinged plate just takes too much power-for holding against a full prop blast at very low speeds.
On some of the large models - ganged servos having in excess of 300-400 in ounces of torque - will not hold against air loads.
That is why the 3D guys use the assists.
My next slide please ----