system
Given the following post, respond as if you're commenting on Reddit:
human
[Harry Potter] Why does money even matter in the Harry Potter universe?

They have magic. It's already been established that you can produce water straight from the wand. You can transfigure something into something else. Oh no, the couch broke? Better transfigure this thumbtack into a brand new couch! The Weasley household was always described as cramped, but in the fourth book Mr. Weasley is able to use magic to make a small tent into essentially a huge tent-castle. So why does money matter if they can just do anything with magic?
gpt
The same reason money exists everywhere else, to procure goods or services from other sources that one might be unable or unwilling to procure by their own means. 

Not everyone is good at everything, some people specialize in areas and it's worth it to have them do it instead of you. For example: Bob is good at potions, and Sally isn't. Sally needs Potion X - she could try brew it herself which might take a long time and/or result in disastrous consequence, *or*, she could pay Bob to do it. 

Some things you are *able* to do, but don't *want* to do if you don't have to: Jessica is an able potionist, but is also an avid researcher of dragons. She needs a flask of Potion Q; however, it takes several months of careful attention to brew the quantity she needs. Jessica *can* create the potion but doesn't *want* to take the time to do it. She'd rather be out in the field studying how what phase of the moon an egg hatched under affects temperament in juvenile Hungarian Horntails (or something like that), so she pays Bob to brew it for her so that she can go do other stuff.

The tent's an example of this: Mr. Weasley didn't enchant the tent himself. Someone good at enchanting somewhere else at some other time enchanted the tent, which was bought by Mr. Weasley's coworker, which was lent to Mr. Weasley.