As spedler said, Dis maps actually alter the mesh. So if you have a shadow falling somewhere in the scene the bumps/ridges etc will show, with bumps while the model itself will look alright the shadow will not show the effects of the bump map.Check the DAZ studio forum over at DAZ. Do a search for Displacement maps and youll see a couple really interesting threads on them. One by Questor and at least one by Stonemason.