The Moment of Inertia (MOI) of any object is as follows. It is a measurement of its resistance to being put in motion around a defined axis of rotation. In essence, Moment of Inertia is a measure of a club’s resistance to angular acceleration or club twisting. MOI comes into play on imperfect contact, when the ball and club face meet away from the sweet spot.
Club MOI Speedmatching as it is called, scientifically makes each club require the same amount of effort or force to swing. The required force can be measured by an MOI machine. What if each club in a set required a different amount of force to swing the club. Essentially this means rotating the club around your body. Then a golfer could not be as consistent. Consistency is difficult to achieve, when each club in the set requires a different amount of force to swing.
More weight distributed in the center of the assembled club will make it have a “low” MOI. Moving the weight away from the center of the club towards both ends will make it have a “high” MOI. A higher MOI will be more resistant to twisting at impact. Mishits will fly straighter. And, the club will be more forgiving when ball contact is made away from the center toward the toe or heel. The club will feel like it has a larger sweet spot. The same is true with the putter. A higher MOI will enable it to be more forgiving.