Well, as the author of the code, you should be able to tell the function what type of variable you expect (string, int, or business entity e.g Book, Bookstore).

Well, as the author of the code, you should be able to tell the function what type of variable you expect (string, int, or business entity e.g Book, Bookstore). That way if you later try to call the function passing an int when it expected a Book, you have an early warning system at compile-time. Not run-time.