If you are hitting a low pitch (like bbscout asked) you have to swing down to the ball, but even so you have to think about the whole swing. It is not way to hit a low pitch with a direct down swing to the ball and hit it in the lower part and have a real good contact. But if you look at a complete swing at that pitch, you start the swing doww but the contact with the ball got it be when your swing is starting to go up. The swing on a low pitch have to be an almost vertical arc, depending if the pitch is inside or outside. Answering the original question, yes, the back spin produces more distance, so in baseball, golf, kicking a field goal in football, or whatever.
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