A lot of teens treat money like it is all the same. If they have it, they spend it. If they want something, they assume they can afford it. But learning to separate needs from wants is the foundation for every other money decision they will make. It is the difference between having money and actually being able to manage it.
This does not mean never having wants. It means being honest about what they actually need first, and then deciding what they want to do with what is left over. That one skill changes everything about how they spend.