I think that good rock molds look more realistic than what I could create by carving cast plaster or from other types of scenery base such as Mold-a-Scene, which is what what I sometimes use. Some rock molds are made by casting actual rock shapes into molds and look more natural to me than anything I could carve from plaster. As far as real rock, it's heavy, and I prefer to keep things lightweight on the layout .
MELGAR