I love Pottermore, which may seem strange considering the number of people disappointed that it’s apparently just some game site (which it isn’t). As a writer, I find it fascinating looking at all of JK Rowling’s thoughts and processes. Actually, I always delight when authors share their writing process with readers. And as writers, sometimes watching other authors talk about their writing and editing process can help with difficult problems like overcoming writer’s block, or learning new approaches to writing and editing.
For instance, on Pottermore those lucky enough to get sorted into Hufflepuff learn that Rowling had initially planned on having Harry Potter visiting all four dormitories during his time at Hogwarts. However, she eventually realized that there was no reason for Harry to be in that part of the Hogwarts. It’s fascinating to learn about, and given the descriptions in the welcome letter and what JK Rowling describes in her thoughts about the common room, it was still as fully realized as the Slytherin, Ravenclaw, and Gryffindor common rooms. Readers just never get a chance to see the Hufflepuff common room because she couldn’t invent an excuse for Harry being there without the trip being out of place within the narrative.
These are often difficult editorial decisions to make. I feel like there is this tendency (a good portion of the time) an intense desire to want to include information about everything, every person and every place in the finest of details. To be honest though, if it’s not necessary to the plot, I couldn’t care less. I’m sure your murderer has some sort of dark, tragic past that makes them a sympathetic character, but if it has no bearing on the plot or why they’re committing the murder, I’m not interested in it. Having that information can be useful when you’re writing characters and locations, it’s something useful to refer to during the writing and editing process. But don’t weigh readers down with unnecessary information. It only makes you look like you’re trying to pad your word count, and for a lot of readers, that’s a huge turn off.
Editing is going to be difficult if you insist on describing and including every nook and cranny of your characters and universe. If you think reading Tolkien’s descriptions are like pulling teeth, or that GRR Martin’s descriptions of the food at feasts are just there for word padding, imagine how much more irritating it’s going to be for readers to slog through passages of descriptions about your universe or characters that have no relevance to the plot. Learning to divorce yourself from some parts of the narrative may be difficult, but your story will flow much better if you can learn to discern which details, descriptions and character backgrounds are worth keeping and which ones are worth leaving out.