It is a sense of meaning. By its nature the saga must have a point, and if the story is successful that point will be powerfully conveyed to the participants. It is even possible for that meaning to influence the participants' lives outside of the story itself, and thus to make a lasting mark on society. But in any case, a well-done arc, once completed, can be the most powerful form of storytelling possible. Each differing part of the arc can give added resonance and meaning to the whole.
Disadvantages are obvious.
The expanded meta-cycle demands a maximum investment of time and skill. All of these forms of story structure are used in roleplaying games. I've run and played in all three types myself. It's fun, the characters are relatively low-maintenance, and it's easy to create a scenario for the campaign. Over that time the characters and world have evolved considerably, with numerous revelations that have required the players to reconsider past events in a new light.