If your on about the little green light on the actual turntable that says pitch control/lock
you need them off to mix, beacause otherwise the pitch is locked on 0. That means it dosnt matter where you have the dial/pitch fader the 2 tunes will never be at the same speed/time because there both locked on 0. Notice that when its on, you can move the dial up and down and the tempo of the tune will stay exactly the same, turn it off and move the dial up and down the tune will get faster and slower.