To perform basic tasks, influence a person or group/s of people, attract customers to a business, etc etc. Simple stuff that you don't need to bother your Guardian for.
I hope i am not talking shit, and please someone might correct me if i am wrong, but i would say your GD is a guide and mentor who should help you in personal development, while a elemental is more like a servant which you command to do several tasks, like influencing people, protect you or people which are important to you, attacking enemies and such...