I did some quick tests.
My conclusion is that any changes on Object properties as Cast shadows or Visible to Refractions/Refractions will create wrong results on top of objects with a Glossiness different that 1,0 (regardless if it is a map or just a number). it will basically show shadows, more or less dense, while Cast Shadows is unchecked.
This is a significant problem in archviz, especially for those planning to create fake shadows or fake reflections inside the 3D scene, to later add objects, like trees, in Photoshop.