Believe it or not, that skill you learned (maybe) in fifth grade or junior high is one of the best friends you can have as a writer. Whether you write fiction, non-fiction, long articles, short blog posts, whole books, or tweet-length ad copy--outlining can pay off ten-fold in better, faster writing. And yes! I'm talking about the old-fashioned, hierarchical, Roman numeral outline.
Simple reason: good thinking leads to good writing, and making an orderly outline forces you to look at thinking instead of words. When done correctly, outlining ensures that ideas/information/characters/events appear in the right order and relationship. That creates flow, and flow makes for good reading.