There are numerous benefits for creating your part design as a multibody part ranging from performance to file management in SOLIDWORKS. However if you have tried to apply a material to a multibody part you will notice that the materials folder of the feature manger will apply the same material to every single body in your design. This works fine if you have a weldment structure which is all made out of steel, but most designs use a combination of materials to accomplish their design goals. In this example for a conveyor belt, there could be aluminum, steel and even rubber. One material could be applied to the entire design, however our mass property and simulation results would be inaccurate.