Peter Burwash pointed out in a Tennis magazine article last year that many club players are better off without the full across-the-body swing of the pros. Specifically, he mentioned that people are misled and don't see how much the pros extend towards the target during the swing. Focusing on the across swing creates weak balls for many players who try to copy the pros but don't have the necessary swing speed or control over the amount of extension and subtle changes needed for direction. He also mentioned the possibility of injuries.
If a player has good swing speed, control, and body rotation, much of the across swing will happen automatically. It is no point forcing it without having the prerequisites.