Legal writing tells a story.
It tells the story in a highly analytical way. That is, it tends to break up circumstances and law into components and reassemble them in an argument or explanation. Each of the law practice formats listed above is designed to channel the story to serve the needs of the recipient. Legal memos and opinion letters cater to the recipient's desire for a clear bottom line supported by reasoning. The appellate briefs address appellate court insistence that one focus on questions of law.