As with any golf club, a putter has a sweet spot. It’s an area in the center of the club where the ball will feel its best when hit from there. Hitting the ball in the center of the putter face is extremely important, as the ball will come off the putter the same straight way every time. This makes it a lot easier to judge the distance and consistently make accurate putts. By hitting the ball off-center of the putting face, it becomes impossible to judge how the ball will react and the distance it will travel.
It is crucial when setting up the putter to lie the ball up right in the centre of the sweet spot. The focus is then to ensure the putter head returns to this exact position when impacting the ball. If one can achieve that, the line of the putts will improve and the pace will become more consistent. The ball will ultimately have better roll and thus less side-spin. Putts with pure roll tend to fall in rather than spin out when they hit the edge of the cup.
If one makes contact with the wrong part of the putter (outside the sweet spot) the putter will either open or close at impact and this will add to the side spin of the ball. This twisting of the putter results in draw or fade spin which causes the ball to seem as though it was pushed or pulled. This is due a phenomenon known as the Magnus Effect which is illustrated below.
When putting most golfers impart a spin to the ball without realizing it. Because of this the ball will have a faster windspeed on one side, which causes low pressure. On the other side however, it has a slower windspeed, which causes higher pressure. This means there is more air pressure on one side than the other which pushes the ball and results in it curving to one side, instead of moving in a straight line. Because of rotation and movement, the air expansion on both sides of the ball is different, so the Magnus Effect appears.
Striking the ball fractions of an inch away from the center of the putter face will damage distance control and speed, because it reduces the efficiency of energy transfer from the club head to the ball. If one doesn’t consistently find the sweet spot, the energy transferred to the golf ball will vary from one stroke to the next.