Antifouling is the ability of specifically designed devices and coatings to remove or prevent biofouling. Antifoul paint is a chemical treatment that’s applied to a hull to make the surface uninhabitable (or at least very undesirable) for aquatic organisms.
Antifouling is necessary on boats that are on the water for any length of time, especially if they’re kept there while not in use. By definition, that’s all boats.