you use the ghost ball to see your spot on your cueball, that is to hit the correct spot on the object ball.
the ghost ball is your cueball following its path to the object ball and placed in the right spot in your mind to show where the cueball will be needed to contact the object ball.
any fool can find the object ball spot that has to be hit to make it go in just by looking at the furthest part of the ball from the pocket or the place where you would hit it if you just shot it in by itself..
that is for learning players. once you can play and have enough under your belt you dont look for a ghost ball every shot as it isnt necessary and might make you more susceptible to choking adding something to the mix not needed.
then it all goes out the window when using english as your spot on the object ball moves accordingly with the english. and that becomes subjective.