Most fictional universes feature stories built around multiple, parallel story threads. There are usually at least 2: the protagonist and the antagonist. But some are built are more than a pair, and sometimes the creators go a little overboard, and that can push something from being entertaining to now being work.
Simple Is Usually Good, But…
Simple stories are usually good. Having a single story thread definitely keeps it simple for the audience. That doesn’t mean the world the story occurs in revolves around that thread, and that thread alone. There are always things happening in parallel, even if they appear mainly in the background. Unless it’s a universe with a single character, there will always be other things happening, some will intersect with the story being told.
Having more than one thread to follow is nice. Done well, it adds depth and texture to the world. It can also be used to create the tension and conflict that stories need as they move forward. Many compelling stories feature a couple of threads, usually more. The Lord of the Rings is an interesting example. It starts with what appears to be a single thread: the escape from Hobbiton, and the creation of the Fellowship. But over the course of the remaining books, the threads split and merge several times, weaving together and pulling apart to meet the needs of the narrative.
It is engaging, and it allows us as the reader to see the story from multiple perspectives. We get to see (and feel) Mordor. The Paths of the Dead are unveiled to us. The Battle of Pelennor Fields gains multiple perspectives. It’s a broad, sweeping story and we get to ride along with multiple heroes on multiple quests.
But Don’t Go Overboard
Just become some is good doesn’t mean more is better. In one TV series I’m watching, this season I count at least 10 (!) parallel, active story lines. Sure, they all share some commonality. And most of the stories are engaging. But some feel tacked-on, thrown in to make the show “relevant” to current events. They aren’t advancing the narrative, and they aren’t providing any real texture or depth to help with world-building. They seem to exist more to appear “politically correct” or “politically relevant” than they do to advance the story itself.
Personally, I don’t mind multiple storylines. Too few and the story feels thin, and lacking in substance. Wondering how all these stories will converge in the end is part of the charm, part of what can make the overall story engaging. But when there are so many that no one story can get enough screen time, or enough time on the page, to really shine is a mistake. It does those story threads a disservice, and that does a disservice to the audience.
I get that finding the balance is tricky. It is tempting to try to explore every thread that could occur, but not all story lines need to be in the foreground. They can be in the background. If you really can’t do that part of the story justice, maybe it needs to remain implied. If it is simply to give some character something to do, maybe they need a different role in the narrative. To paraphrase Sabrina (played by Julia Ormond in Sabrina, 1995): more isn’t always better, sometimes it’s just more.