What Hammer said makes a lot of sense about accuracy. I don't know if you play golf at all, but they teach you when putting to make sure the ball is directly under your eyes, otherwise you are not looking straight down your target line. Same if the ball is under your eyes when release the bowling ball.
On the other hand, like Bill said, it isn't necessary as long as your are doing the same thing every time, it doesn't really matter.
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