Most writers pitch their book at one time or another, either in person or with a query letter. In order to do, you have to be able to label your book. Where will it fit in on the shelves of a bookstore, be it a brick and mortar store or a virtual store?
I remember going to my very first writers' conference having just completed my very first novel. I didn't know it at the time, but it was in a really, rough draft form. I signed up for pitches to an agent and an editor. Before deciding which agent and editor to speak with, I investigated their areas of interest and made sure my book fit into their purview. I had to fit my book into a genre accepted at the time.
The Greater Good. It continues to earn money every month.
I can't fault the agent who didn't want to represent such a book. That was right before the fantasy and paranormal markets took off. But my point was the blending of the two genres, fantasy and romance. So many books today don't fit into exact niches as was once required of them. Many books have multiple genres, paranormal and romance, fantasy and romance, dystopia and fantasy, historical and fantasy, and the list goes on and on. More publishers are open to those blended books, especially smaller presses.
But a writer still needs to categorize their books. Why? Mostly for marketing and promotion. My fantasy books have some romance in but no more so than Robert Jordan's Wheel of Time series. They are epic fantasies. The current romance series I'm working on have a futuristic science fiction setting but they are first a romance. Even though they did better on Amazon as science fiction, they are published by a romance publisher. Two genres blended in different ways and by different percentages.
Every writer needs to be able to label their work both generally and specifically. I write epic fantasy, fantasy romance and science fiction romance. What do you write? Do you have trouble putting your book in a niche? Have you ever read a book promoted as one genre but you felt it should have been labeled as something different?