As I stated before, as a quick change and see how the car felt, I would use the tensioner to make the belt tight, run a handful of laps, and if I liked the feel, I would adjust the diff. I would not recommend running the tensioner all the time tight against the belt. As Skiddins said, it would be another contact point, and if there is that much pressure on it, it could possibly effect handling in a negative way as the tensioner is mounted to the top deck.