It actually plays a very important factor, because the player cannot truly assess the weight of shot that the opponent has hit, this can cause mistiming of the ball, causing you to over hit. Nadal has been caught out by this plenty of times, so calibrating the shot trajectory is much harder, since the sound of the ball coming off the racket mixes in with the ambient noise in the stadium. Indoor conditions will favor Federer without a doubt, if the Fedal semi takes places, and happens under a roof. Federer prefers the elements are taken out of it and said how happy he was when he actually played on the court, even when it was open and commented on there being no wind or even much sun down there. I have watched many matches in Ashe over the years, and I can confidently state that when there was no roof, the wind would get down to court and then move around in a circle, this only got worse the more windier it got. That now does not happen, so the USO will never have that feel again. This works against Nadal, who plays with high margin, and works for Federer, who plays with a lower margin, no wind means, Federer can take the ball how he wishes.