Users who are not experienced in subdivision modelling may have some initial difficulty in understanding the relationship between the proxy and the subdivided model (subsurf). This section aims to give some examples and tips on how to predict what output you will achieve by subdividing different types of geometry.
Proxy: (meaning 'substitute') This is the model that you actually create or draw in SketchUp, on which the Subdivide and Smooth tool will be applied. It is a rough low-poly approximation of the model you are actually trying to achieve, basically a cubic construction with no curves.
Subsurf: (subdivided surface) This is the resultant high poly organic model you obtain when the Subdivide and Smooth tool is applied.
Example 1 - Edges and Curvature
Notice how the number and location of edges in the proxy affect the curvature in the subsurf.
Example 2 - Inner Faces
When you see unexpected 'pinching' in the subsurface, you may want to check for a hidden inner face.
Example 3 - Using the Crease Tool
Creasing edges and vertices allows them to be locked in place. In the figure above, the green vertices and edges have been creased.