The height of the ball, the spin on the ball and the speed of the ball all affect the placement of the ball in the opposite court.
After a lot of playing and practicing, most people generally find a "groove" where they feel comfortable and are able to hit with consistancy, good depth and pace. After a time we no longer have to consciously observe the various "cues" that we needed as we were learning.
As we grow into our strokes, the whole process of creating them becomes more "unconscious"- automatically we add more spin for a sharp angle- hit flatter for a sharp drive to the opposite corner and so on.
Until we get to that point, yes, I believe, it is good to have some sort of reference to assure yourself that your form is intact, your depth is good and your spin is under comtrol.