We recently had an excellent question. The question was, “Do you have to put a sex scene into a book?” What this person is really asking is, “How do you know when to add a scene to a book (or even delete it)?”
It really all comes down to the character. The main character (or characters as the case may be) is the key to the entire story. Everything needs to revolve around him. Everything you use in a scene, whether it’s in the setting or in dialogue or action, needs to advance the character’s journey. The journey starts when the character has a desire for something. The journey is complicated with conflict, and there can be a couple conflicts that pop up along the way. The journey isn’t complete until the character either receives his desire, which makes for a happy ending, or comes to realize he’ll never get what he wants, which makes for a sad ending.
So keep this in mind when you’re thinking about what to add or take out while you’re writing your book.
In the case of sex, does the character learn something new about himself or the person he’s with during the act of sex? In that case, put the scene in because this is where something new is added that will advance the character towards his goal. In the case of romance, sex is usually the stage where the hero and heroine are able to be vulnerable but also safe, and this can add very well to the advancement of the romance. The romance doesn’t have to be the main plot of the book. If you’re writing a fantasy and have a romantic subplot where the two realize they are falling in love during sex, this can work.
Sometimes we get so hung up on sex, we don’t think of other elements to add or not add in a book, such as violence. Let’s say you’re writing a thriller. The killer is a brutal man who shows no mercy. Well, how do you best show it? You have him do something like have our villain break some bones and cut out another person’s tongue. This is showing how bad our “bad guy” really is. That way, you’re showing it. This also advances the plot because the detective will want to stop this.
So when thinking about what to do with a scene, always keep in mind that the scene has to move the character one step forward–or somehow hinder–their goal. If the scene doesn’t do any of that, I would say it’s not necessary.