When working with a player it is very important to educate them on how to handle the racket properly. The consequences can affect the players´ health and performance. The western grip imposes a posture that makes it very difficult to transfer energy from the ground to the ball. The player needs lots of compensation movements to keep the body balanced. He will over-rotate to the outside on the forearm and his elbow.
Karen Khachanov for example needs to make several adjustments with his body to compensate for his grip. From the analysis of his picture, there is no fluidity, easiness, and effortlessness. Just the opposite, a lot of effort, unbalanced positions. The same for players such as Jack Sock, Kyle Edmund, and all of them who opt for this particular grip. Although it may seem that it works perfectly for them, it might limit their results.
The tension generated by these compensations on impact with the ball on daily practice, especially with competitors, can cause serious injuries. Comparing to an ideal model, the player will be losing a lot of acting potential. The ball remains too close to the body and almost aligned with the player’s gravity center, which shortens the leverages.
Kids mostly learn from what their coaches teach them and from the visual observation of their favorite players. Coaches choose the grip according to their knowledge and methods.
The grip used as a kid is the one that will be used throughout the career, with rare exceptions. Let's compare two players with western and eastern grip. Khachanov as an example of the western grip, and Federer of the eastern grip. Two aspects to consider. The racket trajectory and body balance.
On the western grip, the racket moves upwards when the player wants the ball to move forward, opposite to the eastern grip, where both racket and ball are moving in the same direction.
To try to generate power with the western grip, Khachanov has to exaggerate on the upper and lower body rotation. He wastes lots of energy, especially because his body is extremely out of balance and he is not using his full leverage of the arm. He produces big power using a lot of energy. Meanwhile, Federer with a much smaller rotation on the upper body, produces a lot of power, with the body fully balanced, using the full leverage of his hitting arm using less energy.
Taking the picture analysis as an example, Federer, Dimitrov, and others using Eastern grip will appear to be more balanced, hitting the ball with no effort, flowing better at each stroke, and at the same time generating a powerful shot.
In conclusion, the Eastern Grip allows perfectly balanced strokes in almost all positions of the forehand, no matter the court surface. To adapt to individual characteristics, the grip can go as far as a Semi-Western grip without losing control and adaptability. Especially for competitive players, it is an important health factor.