no, you must think that your mod has a body, usually it is the bodywork, everything that is unrelated mesh, without empty, the trim engine considers it the body of your car, so attached to the bodywork, it is therefore not necessary that you make everything related. what must be is also reported on the pipeline, and it depends on how you want to make your car .. example: a mod that does not have animations on the doors, on the hood and on the tailgate, can therefore have these meshes without an empty and the conventional name that the AC motor should recognize.
if you will make a mod with visual damage, then you will have to use empty with mandatory names, for example: FRONT_BUMPER and REAR_BUMPER, which in case of accidents can thus dangle from the body of the car, the same goes for the wings, for the engine hood and tailgate, damage glasses in case you want to put them ...