Originally Posted by southpawboston

Rudi asked a very good question. Assuming the dropouts are perfectly aligned to keep the wheel centered between the chainstays, if you file the leading edge (front edge) of the DO, you will the wheel will point to the left. If you file the trailing (rear) edge of the DO, the wheel will point to the right. Theoretically, both edges should be filed equally to maintain axle alignment. A tiny amount of filing might not sound like a lot, but when you do the math, that can cause the tire's lateral position be several mm between the chainstays.