World Building Is Not Just for Science Fiction and Fantasy

World building is something that you have to do with any kind of fiction. Even if your story set in a small town or a nuclear submarine, the odds that your reader has actually been to that small town are vanishingly small. And so you have just as much work to convince your reader of that a world as you do a fictional world. You can count on your reader having more real life cues to help them along than you necessarily would if you were creating a completely secondary world from scratch.