But seriously, the rules of your world are important. As authors we can't decide half-way through that the sky will shift from a light lavender to neon pink, can we? The Harry Potter dynasty wouldn't be what it is if J.K. Rowling kept changing the rules.
In my writing, the overall world is right here in the beautiful Black Hills of South Dakota. The streets are mostly real (hey, we don't want the bad guys on our REAL streets!) and the terrain is VERY much real. You won't find a swamp here, nor will you find a lake on top of George Washington's head. (Don't know what I'm talking about? Check out the second National Treasure movie.) The things I get to change are in the spirit realm.
And that's OK. For me, that grounds my writing. Sure, I may create a fictional construction company for my victim to work in, but it's on a real street (near two real construction companies, I might add). Is that a good thing? I think so. It ensures that Rapid City natives and visitors alike can believe that Cerri is a real person and really lives here. But no one who works for a certain construction company needs to fear for his or her life, either!
Authors who can't follow the rules of their own worlds are the authors I don't re-read. They're the ones I can't bring myself to recommend to others, either. What about you? Do you expect authors to follow those rules? Or is "anything goes" okay in your reading?