What happens if I don't put "use strict" in a function?

Question

What's the difference following two cases?

Using use strict at the top of the file, not in a function

"use strict";

(function () {
  // ...
})();

Using use strict in the wrapping function

(function () {
  "use strict";
  // ...
})();

I read in a blog post that putting use strict at the top of the file (not in a function) could have unforeseen effects.

Also, from what I remember jshint recommends putting it into a function too.

So, why is it better to have it into a function instead of putting it in the top of the file?