What does the Xcode 5 build setting "Unused Functions" actually do?

Xcode 5 has a build setting called "Unused Functions." I have read elsewhere that "The compiler can never tell if an Objective-C method is truly unused, because it may be called dynamically, either via performSelector:, via subclassing, or many other ways." Given that unused parameters does in fact show parameters that are not being used I was surprised that unused functions does not have the implied behaviors.

Can someone explain what is the meaning/impact of this setting?

It applies to functions, rather than to methods.