Hi Playdo, and actually a plain simple cube (drawn with Draw solid > box) is a special case where it will actually work to leave it as a joined solid and turn on control points. That's because in that particular case all the underlying surfaces share the same control points where they touch each other, the surfaces touch at "natural edges" of their underlying surfaces instead of only at some kind of trim curve edge.

You can turn on control points for a joined-together set of surfaces if all surfaces touch control points with their adajcent ones.

If you do any booleans you will quickly get trim curves created though.

- Michael