Here is How the Gear Effect works: when the ball is struck away from the center of the face and the center of gravity is next to the face (like with an iron) the face moves straight back on this toe hit. (Figure #1)
When the ball is struck away from the center of the face and the center of gravity is moved back away from the face (like a wood) the face moves slightly to the right on a toe hit. (Figure #2)
This puts draw or hook spin on the ball by slightly tilting the spin axis, depending on the severity of the toe hit, the club head speed, and the design of the club. The opposite is true when the ball is hit on the heel.
So this is the reason why the design of the face of metal woods and most hybrids are curved from heel to toe – to take into effect the ball curving left from a toe hit and curving right for a heel hit. The result is that the ball starts to the right on a toe hit and curves back to the hole and to the left on a heel hit and also curves back to the hole.
The Gear Effect Difference for Toe Hit for an Iron versus a Toe Hit with a Wood.
The same gear effect is present on impact points above and below the Center of Gravity when it is away from the face. A ball hit high on the clubface (figure #3) launches higher and with less spin. And a ball hit low on the clubface (figure #4) the ball launches lower and spins more.
The Gear Effect Difference for an Upper Face impact versus a Lower Face Impact on a Metal Wood.
Impact Figure #3
Impact Figure #4
So, how much does non-center impact locations change the ball flight? The following numbers were created by using a robot. The club head design has some effect on how much these numbers change. But they are close to the changes in ball speed, launch angle and spin rate you will experience.
So, you must identify the impact point by marking the face with a Dry Erase Marker. From there you will know how the impact point affected ball speed, launch angle and spin rate and on the spin axis. I believe that impact point is the most under-prioritized of the 4 impact alignments. It is as important as any of them. Failure to accurately know where it is on EVERY SHOT is a big mistake! Almost every golf shot is hit at least a little off of dead center!