Available in the Attribute Editor for object fields only.
Sets where the field emanates from the object. If you turn on Apply Per Vertex, each individual point (CV, particle, vertex) of the chosen object exerts the field equally at full strength. If you turn off Apply Per Vertex, the field is exerted only from the average position of the specified points.
If you are using the Attribute Editor, open the Special Effects section to display the Apply Per Vertex attribute.