Why can't I separate desktop and documents syncing in iCloud?

I would like to include documents in iCloud but not constantly sync my Desktop there. They have two different uses. Documents is a natural place to store, find, and organize your information while Desktop is handy to hold huge temporary staging files (music or video) you have no need to sync. I could create my 'own' Document holding folder named differently but that is counter intuitive. What is the logic to sync both together?

[Re-Titled by Moderator]