There is an optimum CG point where the load on the horizontal stab is zero. This usually happens with the balance point at about 30% of the mean aerodynamim chord. If the CG is farther forward, the plane flies more stably: Less prone to stall, but more sluggish in aerobatics. If the CG is too far aft, the plane will be unstable, to the point possibly of being unflyable (try throwing an arrow backwards...same idea)

Here is one way to test:
Balance per the plans.
Take off and trim the plane for level flight at something less than full throttle. Get some altitude. Place the airplane in a shallow dive.
As the plane increases speed one of three things will happen.
(1) The airplane continues in a straight line as the speed increases. This is good.
(2) The airplane pulls out of the dive all by itself. This means the balance point is too far forward. The Elevator was trimmed to lift the nose a bit in level flight, and as your airspeed increased in the dive, the elevator became more effective and lifted the nose.
(3) The dive steepens all by itself. Balance point too far aft. Reverse of (2) , in this case the elev is trimmed to lift the tail in level flight and forces the nose DOWN with increasing speed.

Here's another way:
Take off and Trim for level flight.
Roll inverted.
If the plane wants a lot of forward stick to maintain altitude, the balance point is too far forward. If the plane tends to climb by itself when inverted, Balnce point is too far aft. Try for a balance point where the plane flies the same inverted as upright.