I have the same question. I have always created sites and terrains in 3ds and exported that into Unreal. Sometimes the sites come from CAD files or Revit files, which is why I take it into 3ds. My problem is when I take that into Unreal, you can’t use all of the same features you can if you build using the terrain tool in Unreal. You can paint foliage, but it is difficult to separate stuff like grass from site objects like sidewalks. There always seems to be a lot of overlap. And you can’t use the nice paint feature on the site for grass and rocks like you can in the terrain tool.