You might have come across the surface deformer in Cinema 4D and thought, what the heck is that for? Don’t all deformers deform a surface? Technically yes, bur the surface deformer can be used to add deformation to an object along the surface of another.
When would you want to do that? Well, TD Aleksey Voznesenski provides a couple of examples. Most predominant, is placing objects on a rig. The surface deformers can be used for buttons, pins, or anything that you want to move and deform with your character.
There are some other uses for the Surface Deformer too, you can use it to add some additional or secondary action to your existing animations. You can see a hint of this before Aleksey changes the order of the deformers.