What is the semantics and functionality of file scope return?

It's all in the title. One part of my coding style is adding return whenever a function with a callback parameter is called, e.g.:

(function() {
    return whatever(function() /* callback */ { // Note the "return" keyword here
        // ...
    });
})();

For quite a while, I have been using the same construct for file scope function calls with a callback parameter, but I wonder if this can cause side-effects I am not aware of.

I could not find any documentation on the subject, and was unable to find out what it does.

Thanks!

[tl;dr] What does using the return keyword mean at file scope and what does it do?