When a Fate Core game reaches a major milestone, it’s a big deal. This is the time when the campaign’s skill cap goes up, refresh increases, or even character’s High Concepts change. It’s the wrap up of multiple arcs, and oftentimes that means the game world (provided the next campaign will be in the same world) may change as well. This is all pretty well covered in Fate Core, so I don’t have a lot to add to it.
If you think about it, though, changing a campaign aspect is a pretty profound thing. It’s just a few words. A short phrase maybe. But going from: