I had the Merchant teach me how to make temporary contracts so that I could show Apollo to everyone. It's also useful that this lets him borrow mana and power from other sources.
It's also possible that one of the girls unlocks spirits-related skills by maintaining a contract with him.
While the chances for that are pretty low since no one has a Gift for taming or interacting with spirits in the first place, having an alternative to simply relying on lucky rolls in the gacha is simply better.
We also found out that Apollo can follow me when I leave and enter the kingdom which seemed to help the Merchant cross out a few theories of his.
As for me, I was glad to have made a contract with a spirit since it allowed me to take a peek into a world I was pretty unfamiliar with as there was no point in even looking into it to begin with.
