Underbody Coating

Modern automotive coating methods consist of five main steps. They include the following:
Pretreatment: removes and cleans excess metal and forms an appropriate surface structure. Enabling bonding of a corrosion protection layer.
The next step is electrodeposition (ED) of the anti-corrosion or rust prevention layer.
A sealer like Poly Vinyl Chloride (PVC) is applied for anti-corrosion, elimination of water leaks, and minimization of chipping and vibrational noise.
A primer is then applied to promote adhesion between the surface and the basecoat; it also imparts a smoother surface for subsequent layers and has anti-chipping properties.
Finally, the topcoats that include a basecoat and clearcoat are applied; they provide surface properties that are sought after, including color, appearance, gloss, smoothness, and weather resistance

The above process's first four steps are collectively called undercoating or under-body coating.
The advantages of Undercoating include:
Corrosion protection and Reduced wear and tear, there aren't any disadvantages too.