It prevents you from having to topologically sort your definitions, or otherwise declare everything at the top. Since idiomatic C uses header files, though, it

It prevents you from having to topologically sort your definitions, or otherwise declare everything at the top. Since idiomatic C uses header files, though, it doesn't matter too much. Main benefit is that non-public implementation details (e.g. static functions) needn't be declared at the top of the source file.