Interesting. I don't need a Silmarillion because I'm sticking to hard-sci-fi (my fave) where reality and logic prevail. I still appreciate fantasy and myth and stuff but I have no need for monsters, magic, and bad physics. However, I have a backstory of development to the events in the story to lend it gravitas, history, and rational reasons for things being as they are - and I need to seamlessly weave that in naturally without seeming like obvious exposition. Many of my threads will inevitably end up on the editing floor.