This is why. We all see pros hit harder, make better, more accurate shots. And, when you have the physical size that a pro has, you start to really wonder how much is in a "pro racquet", and how much is them. Well, let me tell you, it is all in the weight and to a lesser extent, balance, of a racquet. I weighted down my wilson tour 90 to 13.5 oz and made the frame basically an even frame like Sampras had(though his was slightly heavier and had a smaller head), and, this is important, with not much technique change, basically the same strokes. Serves, about the same speed, no change. Groundstrokes=insane amount of more power. And, what i mean about power, is not power going out of bounds uncontrollable power, but penetrating, driving power from the ball gettting pummeled by a much heavier object. Volleys=night and day better, no form change.. Why?.. physics again, a heavier frame flattens that tennis ball out and keeps it from jumping off the racquet and causing it to sail. So, i can really DRIVE my volleys hard into the court. Approach shots=night and day difference.. with no grip change my short ball troubles are WAYY over since now i can drive a ball harder with the SAME STROKE, keep it from floating, and make it a winner or a winner off the next easy volley. Also, with the "new frame" I can volley better from farther back because the racquet gives soo much more velocity to the ball. And, my backhand?.. Used to be my weakness, now, with the same form, i can pummel backhands that used to land short, and they have soo much pace on them i would swear they came from my forehand or i was lefty!
Now when i hit my other 2 same frames that i haven't weighted down yet, they feel like feathers(at probably 12 to 12.5 oz), and i feel the ball float or not stick and not have nearly the same velocity on shots. Also, my forearm, and body used to be "late", and still sometimes is when warming up. But, now my forearm just automatically makes a stronger contraction to handle and swing the heavier frame.
Yet, again, everybody is right when they say you could not swing a pro frame. If you are an armswinger, and never learned to use your body to make power, don't even think about it(and, that counts for about 90 percent plus of people i see hit the tennis ball). Your arm will wear out quick and you may get injuries hitting the ball late. I adjusted my serve to get more shoulder turn, so not to use as much arm and much more body, and my consistency and power are up also.
So, bottome line, if you have good biomechanics and always wanted to hit a ball like the pros, do it. If you are an armswinger you can try it, but if your arm rips off, don't blame me. (I put the weights in the 10 and 2 positions, though i believe it was just important to get more weight in the hoop to achieve the proper total weight of the frame and also to achieve an even balanced frame vs the tour 90's head light balance)