Car Wheel or Motorcycle Wheel always being plated because it will look better and bright also to prevent from corrode because of often contact with water, and other dirt or waste. It must use Electroplating Process use metal better than the original metal can prevent from corrode like chromium. So car wheel use chromium plating.
For soldier helmet being chromium plating may in order look grate and to prevent from corrode. On the practice usually just using paint is enough.
Coated with brass usually not using electroplating but just spray to the part and rubbed with cloth. But this method can make brass strong stick to the material. By electroplating process make brass stronger stick to the material, and it is look like gold plating.
Gold Plating or people said gilding, gold plating usually use for jewelry because it look like gold but cheaper. Part with gold plating usually will use in special application, may the environment very corroded so it need noble material to coated, like gold or silver.