A lot of pros will look at the hole and putt, but typically never all the time. I'm not sure why they don't do this more often as it's the more natural way we aim anything. For me, looking at the hole has been a significant stroke saver with my short putts. Anything inside 10 feet, I look at the hole. Outside that, I mostly look at the ball, but not always. It's got to feel right. If you don't believe looking at the hole is more accurate and reliable, try this exercise. Take two golf ball on the practice green and place them about 3 feet apart. Stroke the first one into the other with enough force to knock the target ball at least 3 to 4 feet away. Repeat. Try this a dozen times while looking at the target ball as if it was the hole. Then try it a dozen times using the more traditional method of looking down at the ball you are stroking and not looking at the target ball. I think you will find your answer quickly as to which method is more accurate and consistent. As an added benefit, when you do putt to a cup, it will look to you like a bushel basket.