Subdivision surfaces combine the best features of NURBS and polygonal modeling and are useful for intricate surfaces such as faces. Using subdivision surfaces, you can model complex characters and create models from single primitives (as in polygonal modeling) but with perfectly smooth surfaces (as in NURBS modeling).
Like lattices, subdivision surfaces rely on varying levels of editing detail that allow you to adjust a surface from a global level, where large parts of the model are modified, to a micro level, where you have control over the most dense surface points.
Typical subdivision workflow begins when you create a simple polygonal mesh of your model. The polygon is converted to a subdivision surface that you can edit using any number of subdivision detail levels. More often than not, the resulting subdivision surface is then converted back to a polygonal object for use in production. Subdivision surfaces can also be converted to NURBS patches.
The Subdivision Surfaces (or SubD, as they’re called) toolset is found in the Surfaces menu set (press F4). You’ll find yourself switching back and forth within the Polygons menu set (press F3). Just remember these hotkeys, and you’ll be switching like a pro in no time.