Question: I am currently writing a story that takes place in a massive fantasy world. I have three main characters that play a major role with in the story. I was thinking that the reader can pick one of the characters and read their individual journey. along they way they can choose, with the options I give them, what happens next in the story. I think this has been done before, but is it a good idea to do so, or would it be too much unnecessary work? Thanks for reading!
It has been done before, mostly in children's and juvenile literature (as in the Choose Your Own Adventure series). It's also how many video or role playing games work. I've never seen it done in a serious work of fiction, though perhaps someone will do it eventually.
The challenge is that it can be hard enough to create a really good story in which all the events unfold in an emotionally satisfying way and the characters and themes are explored in depth.
In a "choose your own" book, the task is harder because you have to design multiple stories/pathways. For them all to be emotionally satisfying works of literature would be a very difficult task. (For instance, how would you foreshadow multiple endings?) Also, such a book would be many times longer than most novels, since it would have to contain many stories.
It is for these reasons that "choose your own" books are usually done as children's books. In children's books, the plots, theme, and characterization can be very simple. The plots tend to be more like short stories than novels, to keep the book from becoming too thick. In most video games, the better the story is, the fewer real options the player can choose from among.
If you want to write your novel using multiple point-of-view characters, each with his/her own story that intertwines with the others, great. But I suspect if you fully develop one version of each of these plotlines, that will prove to be a big enough task.