Hi Felix, one other thing I should mention is that showing control points itself (not necessarily shrinking surfaces) can be useful as a sort of diagnostic function to try and get some more information about the structure of a surface.

For example if something is not behaving right one of the things I will usually do is to view the control points of the surfaces to see if I can find any warning flags like strange clusterings of points or stuff like that.

Don't know if that applies to what you are asking about...

- Michael