Is not the question; what to heed
Is what to let your reader see
And how much back story you need.
Never give too much back information all in one go. Drip feed it in to your story so your readers absorb it. If it’s done as one big block, it will stick out as a huge amount of narrative, the bits people tend to “skip”. Also don’t give away every single bit of detail. As a reader, I like working things out about characters and later finding out whether I’m right or not. All I need are the appropriate clues!
Ideas can be fleshed out in outlines
Which can save many an author’s whines
As it helps you stay on tangent
You write what you originally meant.
I use an outline for most of what I write now. I find an outline helps me not to repeat myself and if I get a “brilliant” idea while writing, I can look at my outline and see if it can fit in or improve this section and add it in accordingly. I do tend to overwrite and the outline helps me stick to the point. I don’t go into minute details but give myself enough information to get started, to see where the story is heading and what the ending will be, giving me room to expand ideas. It’s also nice being able to see yourself work through an outline as you write your story and see how you’re making progress.