But at a higher level, what is checking if it exists, and why? What is the user looking at on the front end that requires that client to ask us this information? I can see the case for wanting to know what content group this particular user belongs to for this piece of content. I could see the case for finding other people in the group, etc. But I don't see where this particular call connects back to a concrete use case.

My higher level concern is whether this is an encapsulated API that understands domain-level questions, or whether it's being treated as a dumb CRUD store for something smarter being built on the consumer side.