The Master Point controller controls point sub-objects within editable splines, editable surfaces, and FFD (free-form deformation) modifiers.
The Master Point controller is assigned automatically whenever control points, vertices, or vectors (tangent handles) are animated in the sub-object mode of an Editable Spline, Editable Patch, Editable Mesh, Editable Poly, NURBS surface, or FFD (Free-Form Deformation). By allowing you to select and move all the sub keys, visually correlate keys to points in the viewports, and change key properties quickly, this controller helps to manage the numerous tracks created when animating vertices, control points, and vectors.
The Master Point controller is displayed as a track with green keys in Track View. Sub tracks below the Master track contain all the animated vertices, control points, and vectors.
Example: To animate vertices, viewing the Master Point controller track:
3ds Max opens the Track View - Curve Editor. At the top of the Controller window, you can see the tracks for the sphere.
Track View displays the Master Point Controller track, with tracks for the animated vertices below it.
With Track View in Dope Sheet mode, right-click a green master key of a Master Point controller to open the Master Track Key Info dialog.