How to distinguish solidBodyMotionFvMesh and dynamicMotionSolverFvMesh
 

I am confused on the difference between solidBodyMotionFvMesh and the dynamicMotionSolverFvMesh. On the openFoamwiki, I found the definitions of them as follows:

solidBodyMotionFvMesh: Prescribed mesh motion. No topology change in mesh.
dynamicMotionSolverFvMesh: Mesh motion based on solved mesh motion for rigid body motion.

And then I found that the tutorials case: propeller (under pimpleFoam) is using dynamicMotionSolverFvMesh. Here is my question:

Isn't the motion of the propeller prescribed? We know how the propeller moves (rotates at a certain velocity) before we run the mesh and the simulation. Then why should we use dynamicMotionSolverFvMesh, instead of solidBodyMotionFvMesh? Could anyone explain this to me? Thanks in advanced.