This simple technique is useful for animation. In fact, I redid the smoothing part of Anna, by changing from subdiv proxy to mesh smooth. When animating a character it is good to have the choice of displaying either the high-res or low-res model.

Following [2] what I did was to create a smooth custom attribute on the Anna's master node, with min 0, max 3, and default 0. Then I did a Mesh->Smooth on Anna's character, dress and hair. Using connection editor, I connected the smooth attribute to the polySmoothFace's Divisions attribute for each of character, dress and hair polygonal mesh.

So now, it is very easy to just switch between the low-res and hi-res model.

References
  1. Learning Autodesk Maya 2008 p. 301-302
  2. Learning Autodesk Maya 2008 p. 416-417