In different software they called differently: empties, nulls, locators, etc; but the idea stays the same – to organize objects hierarchy in you scenes. Think of it as of folders in you operating system, or boxes on which you put labels and can conveniently store and transport a bunch of objects inside of them.
As obvious as this tip might seem, throughout my CG experience I can tell, that project, where everything named and organised properly is more like an exception to the rules. And that’s no surprise, knowing how infinitely lazy human beings are.