FFD works best on models that are "dense." A simple cube has only 8 corners. If you apply FFD to a cube, the control cage only has those 8 points to pull—resulting in a blocky, faceted mess. : Before applying FFD, use SketchUp’s native "Subdivide" tools or an extension to slice your model into many smaller faces. The more vertices your model has, the smoother the FFD deformation will be.
Best use cases
What are you trying to model with it? Share public link sketchy ffd sketchup plugin