Comment by alextingle

The only difference between "" and <> is that the former adds the current file's directory to the beginning of the search path.

So the only reason to use "" instead of <> is when you need that behaviour, because the dependency is relative to the current file.

If you use "" in any other situation, then you are introducing a potential error, because now someone can change the meaning of your code simply by creating a file with a name and location that happens to match your dependency.

(Yes, some compilers have -isystem and -iquote which modify that behaviour, but those options are not standard, and can't be relied upon. I'd strongly advise against their use.)