The bias point was added to allow influencing intersection points for: arcs and ellipses - lines, line strings, and shapes. The default behavior prior only provided the intersection point at the furthest vector length. Users requested a way to optionally provide a bias point having less magnitude (distance) than the furthest intersection point yet still a valid intersecting point for that element. This helps with cases where a shape has multiple intersection points with the intersect vector and you don't want the default furthest segment intersection, but a segment closer in magnitude to the origin of the vector.
Please note ProjectPointOnPerpendicular1 help topic also provides an "Example" hyperlink located at the top of the page providing two code snips that you can use to validate proper operation of the function. The code sample provides code snips to test against target shape and ellipse elements.
Also, the post: (ProjectPointOnPerpendicular2 - not working as expected ...; may help understand differences between use cases for ProjectPointOnPerpendicular1 and ProjectPointOnPerpendicular2.
HTH,
Bob