To avoid #backpain, #Hippain and #kneepain it is important to have a vertical bar path during #squatting to make sure the force of the weight is equally distributed. .
This video shows that you want to have the weight over your mid foot for better balance and safety.
If the bar path is too far forward, the center of gravity is forward and you load your knees as well as your back. If you are too much on your heels you might be more unsteady and that is not safe while lifting heavy loads.