Mark Garaway claims and I reckon there is some truth in that the full rotation of the bowling arm helps to generate more over-spin and therefore dip. Probably if combined with a vertical arm or a near vertical arm when attempting to present the seam upright in the style of a classic top-spinner or a very small turning Leg Break. Have a look at the video here of me practicing with and without a ball in my hand running up to the start of the season here in England. I'm not getting it right when the balls in my hand at the moment, but the action becomes very different when I've not got the ball. Note how my arm comes over and ends up at my pocket as Garaway says. In fact my arm goes further without the ball. But then look at it with the ball... It doesn't complete the full circle in the first slo-mo sequence it ends up in front of my body and I abruptly stop. I think it's this aspect of the action you need to avoid, a smooth fluid movement with the arm coming right through is the desired affect and helps put more spin on the ball by my reckoning.