What is the point of them? I understand that they drain magika/stamina, but as a level 9 mage I destroy things with dual flames before they can even touch me. Will they be more useful later on?

It also depends on what you're fighting. Undead tend to be weak to fire. Dunmer are strong against it. Many dragons are strong against fire or ice. Daedra used to be weak to electricity, I don't know if that holds.

Lightning is also the fastest one. It's better for longer ranges.