It all depends on how immersed your world is in the elements of that genre.
The world is just like the one we see, except the hero, the villain, and maybe some friends have a special power. Perhaps they can see through walls or have an accelerated healing factor. Other than this, the world that the story takes place in is no different than ours. Some examples of this are “The Sixth Sense” or any Spider-man movie.
The story world is identical to ours, except that there is a major change. This is the basis for most alien invasion, vampire attack, or zombie films. “Buffy the Vampire Slayer” and “The Walking Dead” are television shows that do this well. Other examples are stories involving characters like Superman, the X-Men, Transformers, and Harry Potter.
The Secondary World
The story takes place on a completely different world. The geography, climate, politics, economy, and species of life are specific to this setting. This gives the author complete control, but carries the burden of making it seem real to the reader. Obvious examples are “Star Wars” and The Lord of the Rings.
The Strange Visitor
The fourth type of fantasy or science fiction setting is when a person from our world visits another time/space or when someone from a different time/space visits our world. Alice in Wonderland, The Chronicles of Narnia, Peter Pan, and “The Terminator” all fit this type perfectly.
With a better understanding of the different types of fantasy and science fiction settings, it will be easier to distinguish which best fits the story an author is trying to tell.