DaveFace: Yeah, I’m also a long time CryEngine user and I was expecting this working in the same way in Unreal4 
Basically, if you use DefferedDecal material, it works only with Decal Actors, but if applied to geometry it doesn’t render. Btw for chipped edges you can use just a masked material and Push modifier in Max, then attach it to your main mesh with another material ID. But z-fighing may become a real issue here at greater distances, whereas decal shader would “know” to stay on top.
TheJamsh: I think what you meant was volumetric decals. And yes those are probably really expensive.
Maybe there’s some config setting which can enable this functionality? It looks like Decal actor is basically a plane, and all that’s needed is for shader to work with custom geometry, the rest works great. As I said, I can setup examples of where this is crucial to get good and flexible results, but I think the example that DaveFace posted (chipped edges), is a very common use for it.