Most balls come in one standard size and the rules of golf do state a minimum and a maximum diameter of ball. The size of the ball will determine the rate of spin more than anything else. The larger the diameter of any circle, the slower the outside of that circle will spin. Therefor, a ball such as the Topflight Magna (which is the most recognized oversized golf ball) will have a slower spin rate than say a regular sized ball, when hit with the same swing. This is good and bad.
Good because, for most golfers a large problem is the slice or the hook which is a result of producing side spin on the ball during the shot. The larger ball will have less spin and therefor curve left or right less than a smaller ball.
Bad due to the increased wind resistance. The larger ball will create more drag upon the surrounding air and therefor not fly as far. Bad because a well struck shot will not have the same backspin as a smaller ball would and therefor be less likely to stop quickly on the green. Good along the same lines because the ball hit down the middle of the fairway will have less backspin and continue to roll further than a ball which has more backspin.