If you complete the full Underground mode, you will also unlock all body parts, all rims, all accessories, all paint colors, all decals, all vinyl, all neons, all NOS packages, all drivetrain packages, and all exhaust packages.
Just like when you buy a car, taking the used golf cart for a test drive is a good way to see how it drives and the engine or drivetrain is still in good working order.
You can now sort your collection by country, drivetrain and manufacturer, which can save loads of time when you're looking for that one car to enter a specific race.
