One of the writers I coach asked me whether I plan my writing. The answer is both not at all and all the time. I think of planning as World Building. It includes research, planning, plotting, map making, genealogies etc. However, this is not all accomplished before I start writing. Much of it cannot be accomplished if I am not writing.
I don't know where a story is going until I have written it. Sometimes I only know a few scenes. Other times, I have a big idea which is too large to explain and has no story. Once I have draft, I have a decent idea about the story. However to put this draft on paper, I have to take breaks to reflect, research, and plan. With each edit it, characters and the plot change. The story is ever evolving.
During my MA, I wrote an outline of a novel for the first time. In order to write the outline, I had to write several drafts of two stories, create a complex genealogy, and wrestle through many versions of the outline. It ended up being for 12 linked short stories.
When I started writing, I put the outline in a drawer and only looked at it for characters names and a few details. I wrote the first 40,000 words of a novel with nine interlinked stories. The blood sweat and tears that went into the outline paid off, but the final story had little in common with the outline.
This novel will continue to change as I write. Once I finish the first draft, I will know where the story is going. This will likely mean an extensive edit to the beginning so it agrees with the end. This is not a problem. It takes time to get familiar with characters and their stories. The end product should be worth it.