Changes the existing polygon component selection to the vertices that are associated with the components originally selected.
For example, if you have a polygon mesh comprised of four-sided polygons (quads) with several faces selected and then choose Select > Convert Selection > To Vertices, the selection is converted to the vertices associated with the previously selected faces.
Tip:
Many of the convert selection features are available from the context sensitive polygon marking menu when you press 
+ 
whenever a polygon component is selected.