Usefulness of the iOS app?

I use Mac, Windows, and iOS. What I do is a variant of what Teriodin describes, but I use OneDrive and Dropbox (although you can substitute iCloud for where I am using OneDrive):

  1. On my PC and Windows, I have the Dropbox and OneDrive clients installed, so I have my “Dropbox folder” and my “OneDrive folder.” I am using a free Dropbox account.
  2. I have the OneDrive client installed on my iOS device. I do not have the Dropbox client installed on iOS, as doing so would take one of my three free device slots.
  3. I save my active projects to Dropbox\Apps\Scrivener. This is the location I open and edit these projects from on the PC and Mac. Scrivener on iOS syncs this location by default and sees all of the projects I have there. I make sure to wait for Dropbox to fully sync before I open a project on any device, and after I close on any device. Each project is only open on one device at a time. In iOS Scrivener, I manually scan the directory before and after working on each project to ensure the changes get written back to the cloud.
  4. Once a project becomes inactive, I move it (on my PC or Mac) from Dropbox\Apps\Scrivener to OneDrive\WritingArchive and wait for Dropbox and OneDrive to fully sync the change. This folder is the archive of all of my projects that are currently inactive. (I use this to keep my active projects folder on Dropbox as small as possible, which makes sync times faster.) Conversely, if an inactive project becomes active, I move it (on my PC or Mac) from OneDrive\WritingArchive to Dropbox\Apps\Scrivener and wait for Dropbox and OneDrive to fully sync the change.
  5. I have a OneDrive\WritingBackups folder. Scrivener on Mac and PC are set to create an unlimited number of backups there, as a single ZIP file, with the date/time stamp in the file name. (I have 1TB of storage on OneDrive, so keeping things here indefinitely doesn’t affect my Dropbox quota, AND allows me to manually find my latest backups if Dropbox is down.)

Most of the time, this is very automatic for me and I don’t have to think. I simply make sure Dropbox and OneDrive are up-to-date, open the active project in Scrivener, do my work, close the project, and wait for the sync clients to show they are up-to-date. On iOS, I open Scrivener, sync the directory, open the desired project and work on it, then close the project and sync the directory again before I close Scrivener.

If I ever need to access my backups for any reason, I can do so from any machine (using the Files app on iOS to move projects around.)