and usually, they do a good job on setting the lines...correct?
So, common sense would tell you if I get to move the lines by 10 points, it greatly helps my chance of winning. 10 points in football is alot. I think my percentage of being correct with the 10 points added outweighs the percentage of my losing by adding games.
Hell, there is a 50% chance of someone being correct on every game. By adding 10 points, I think that number goes up significantly.