Lets you edit the next finer subdivision surface level if it currently exists. If a finder subdivision surface level does not exist, the Refine Selected Components feature increases the level of detail possible for a subdivision surface by adding one level of refinement to the subdivision surface based on the components that were originally selected.

For example, if three faces are selected on a subdivision surface and you then select Refine Selected Components, a level of refinement is added to the regions contained within the three selected faces on the surface. That is, additional faces get added to that region on the subdivision surface.

This lets you add increasingly finer features and details to a subdivision surface in the regions that require it. If you require further detail, simply select Refine Selected Components again with the components still selected and additional detail will be added to the selected area.