I see this around the blogosphere a lot. When do you need backstory? Only use as many descriptive words as are necessary. I need to include more characterization. Only include exposition when it is necessary to the plot. I need to learn to show not tell. Don't include anything in your book that isn't 100% necessary, cut out everything else. And many more iterations of the same basic idea.
Well, I'm here to tell you that the idea of what is and is not necessary in your story is a False Dilemma.
Elements of story (like backstory, prologue, characterization), building blocks of writing (like exposition, descriptive words, dialogue) or even specific elements of your story (a certain character, a particular scene, a paragraph of description) are not either necessary or unnecessary. Because let's face it, this is fiction. And there's no such thing as "necessary" in fiction. Everything is unnecessary include your entire story its self. Every word, every sentence, ever character, every plot point is essentially unnecessary.
But that's ok because the point of reading fiction is not what is "necessary" but what is pleasurable. Fiction is entertainment or possibly even art. You don't ask yourself "is this necessary" when writing. You ask yourself "does this make for an enjoyable reading experience".
Now you're down to the question of what is enjoyable, which is much better. As we all know, this is going to be subjective and trying to please everybody will only please nobody. My personal opinion is that the author needs to write the story that they would enjoy themselves.
So if you like backstory, then include it. If you like a certain plot point, include it. If a certain descriptive phrase is pleasurable to your ear, include it. If you think a certain plot point make the story more enjoyable, include it. And so on. Don't be intimidated by the idea of what is "necessary". Focus on what is fun and pleasurable and beautiful.
