Having the prototype available before the first use of the function allows the compiler to check that the correct number and type of arguments are used in the function call and that the returned value, if any, is being used reasonably. The function definition itself can act as an implicit function declaration.
While shellac is not usually the finish paint choice, it is often thought of as the best paint primer available. It has properties that oil and water based paints can't match, and provides a more dependable seal than most other primers are able to provide.
Also, base coat/clearcoat systems will dry quick enough, but single-stage paints have to sit overnight.. Cost savings seem to be the major reason to choose acrylic enamel over urethane, most restorers told us. Thus, quick in-and-out commercial auto painters choose acrylic enamel for entire-body paint.