When you say you're hosting Lemmy [0] for a fan site does that mean you're hosting it for others to use? How/why did you pick Lemmy? What's your experience with it so far?
Being federated allows them to use their existing identity or create one for the fediverse, and general or like minded communities to see the discussions as well. The same reason people use subreddits for fanbases, but not being beholden to reddit.