If you have a solid object like a car that you want to use and no sub-part of it needs to be animated, then importing the object as a "prop" and using it that way is easier and faster than converting it to a model.
If you need some solid part, like a door, to also animate then one would break the car model into two parts, the car and the door and import them as separate props and use them that way in your chor. That would save remodeling... IF you have the program the original model was made in and can break the polygon model there.