When to re-balance a motor?

My concern is based more on what I have been reading, and that is the fact that although 1 gram is not much, due to the laws of physics, its effective weight at a high RPM speed is multiplied many times over. 28 grams = 1 ounce

From engine builder mag:
Maintaining Your Balance: Engine Building Tips to Reduce NVH and Increase Life - Engine Builder Magazine

The centripetal forces generated by any imbalance increases exponentially in proportion to speed. Double the rpms and you quadruple the force. A 2 oz.-in. (ounce-inch) imbalance on a crankshaft will generate only about 14 pounds of centripetal force at 2,000 rpm. But when the engine revs to 8,000 rpm, that slight imbalance now becomes a pounding force of 227 pounds!