I would argue that offering fans a template goes miles towards to how… sandboxy the series becomes. (For want of a better term)

For Harry Potter, it was the whole academic experience. How you got admitted, the personality tests; things that enable a safe starting point and allow the fans to go in their own direction.

With Kingdom Hearts back in the day, it was Organization OCs with powers and weapons that followed a template. Similar with Steven Universe and minerals and weapons.