There are two types of balance, aerodynamic and static. What you seem to be discussing is aerodynamic balance although it is easy to also have a good static balance by weighting the portion forward of the hinge line enough to balance out the weight aft of the hinge line. The static balance helps to negate the effect of G forces while the aerodynamic balance allows a servo to have more effect for each unit of force it applies to the moveable surface. Just be careful that the area ahead of the hinge line does not exceed about 20% of the area aft of the hinge line else the surface will tend to hunt (swing or oscillate about the neutral position) to the point where it can actually become uncontrollable. Properly set up, you can reliably use very weak servos on a fairly large model when required.