Force Displacement has no effect on the planet. And the "force" just means it is rendering it with the non-raytracing rendering method, there is nothing really "forced" about it.
It's true though that the non-raytraced rendering method does not produce quality that is as high, which is why ray-tracing is the default and considered best method. It can't do displacement at present though, which again is what the "force" mode is for (which, to reiterate, only works on non-displaceable objects; some native objects in TG like the Planet, Sphere, and newer displaceable Cube are all natively displaceable and shouldn't have the "Force" option).
- Oshyan