The vanishing point is an important part of linear perspective. The scientific approach to linear perspective is predicated on lines that converge to one or more vanishing points.
In this work by Piero della Francesca the red lines clearly show how the lines all meet at one point. Note that it is not important that the vanishing point be seen. Nor is it important that the vanishing point be placed in the center part of the work, as can be seen in this work by Canaletto.