I watched a video on you tube (I think) about depowering the main. It was about racing mind you, and it was very poor quality, so it was hard to hear the explanations. Basically, they would tension or lift the topping when ever they moved the main. For instance, if they were dropping the traveler, they would tension the topping, move the traveler, then slack the topping again. I don't know why, and they didn't explain, and I don't know if its correct. I have never done it that way. It may just be an ease of movement thing when the main is under a lot of load.
Great men always have too much sail up. - Christopher Buckley
Vaya con Dios