Big hitting is as much about rhythm and timing as anything. This is why a 120 pound female player like Sania Mirza can crush the ball. So where is rhythm and timing most obvious among top level strokes? I say it is largely in the takeback.

On the right are two world class players, Florent Serra and Alejandro Falla. Notice how they both have a loop takeback. First the arm and racket lift upward. Then the arm extends backwards by opening up at the elbow. Then the arm and racket fall together. I want to point out a few advantages to this takeback (rather than taking the racket back quickly or "prepare as fast as you can" idea that is common).

1. First, there is a natural rhythm built into this loop because a) the racket never stops moving and b) gravity becomes a source of natural, "free" momentum as the arm and racket drop
2. We know, according to Newton's First Law that "An object at rest tends to stay at rest and an object in motion tends to stay in motion". Once you stop your racket and wait, you have to overcome Newton's first law to get things moving again. That is why top players NEVER stop moving their arm and racket once they start their takebacks.
3. A loop takeback lets you hit both high balls and low balls. As the ball comes towards you, it can rise faster than you thought, or it can stay down lower than you thought. A looped takeback let's you adjust because the arm and racket first go up and then can drop as little or a far as you want. If you take the racket straight back, it becomes very hard to work with balls at varying heights.
4. Top level forehands all look like a "Figure 8"<> from takeback to follow through. The looped takeback is an essential part of this overall flowing motion. Here is a great exercise I found years ago to practice to get this overall "Figure 8" motion. It's from USPTA pro Lee Couillard.