In older times the ball was adressed squarely with the strings.
In modern tennis you approach the ball with the racquet’s frame, the upper edge, starting from below the ball for topspin, the lower edge, starting from above for slice.
Tennis today is more of brushing, massaging, deflecting the ball.
Not only is contact longer in this fashion, it also elicits spins and more control.
Power is no longer the main consideration. Modern racquets and strings have great response and generate ball speed with a lesser effort that racquets of old.
Even further, when you are looking at the ball you are about to strike, having the edges in mind increases your awareness of the racquet angle, especially of the vertical angle that determines the height of your shot.
It is almost as if playing tennis with the hand. The fingers have feel, have awareness. The racquet has not.
Oscar Wegner Modern Tennis Methodology