If the terrain behind is e.g. not in great detail, angles (normals) and heights may not need to be calculated. Like for veggie altitude restraints, slope colors, etc. But you'd have to do some testing. In my mountain path I did use a compute normal and an XYZ shader, but no compute terrain. Sometimes you can even get away without any compute, just try it out. But like smoothing in a fake stone layer is then not possible, it'll smooth the whole planet. But maybe smoothing isn't necessary, etc. Experiment a little and compare render times and visual check differences with or without the compute terrain.