What are the implications of "-Wauto-import" in Xcode / Clang?

Question

While playing with -WerrorI encountered -Wauto-import. I seem to believe that all tags #importthat import system libraries / frameworks into @import statements. Is a warning useful only to use modules explicitly or are there other consequences?

Example

#include <stddef.h>
// suggests change to 
@import Darwin.C.stddef;

Oddly enough, if I agree with the proposed replacement, I get a warning expected unqualified-id