I agree that any sync service (or app with internet access) possibly brings with it all of the inherent issues mentioned above.
But what I really meant was that the more apps and sync services a user has running concurrently, the greater the chances are that something will fail.
So if service A works well, adding service B might be detrimental all round.
The OP has iCloud and it works for them. No imperative need for them to replace or augment what already works. If iCloud plays up, then service B can be called on.
Apologies, again, if I have still misunderstood. Just trying to support the OP in making any choice they think best. They are right: there is no need for them to use Dropbox.
On that we agree entirely! The only people who might want to run both (or Dropbox and something else entirely) are those that use iOS and really prefer to sync directly rather than use one of the other many methods for doing so.
I apologize: I know this is an often debated issue, and the manual is very extensive on it, but I still need a very concise and clear answer. I admit I’m victim of a surcharge of information.
Use case: I want to work on a project on two Macs. No other odd machinery involved.
Solution: Is it correct that I can put the project in iCloud Drive, and work in the following way on it?
Open it on Mac A. Edit, close it.
Open it on Mac B. Edit, close it.
Have automatic backups on both Mac A and B, to be sure you can recover in case of need.
Additionally: In the Finder of both Macs, should I check right-click on project file > Keep Downloaded? Or is it totally ininfluent, since the project is already backed up by the Apple servers, and locally by the automatic backup made by Scrivener?
A memo to myself: this can be avoided by telling the operating system not to delete the files in iCloud Drive. This can be done with a hidden preference in:
System Settings > [personal account] > iCloud > Saved on iCloud > Show All > iCloud Drive
While in this dialog, switch off the muddily named Optimize Mac Storage option. This will prevent the files to be automatically deleted from the Mac.
Actually, it does the opposite. Preventing your local files from getting “optimized away” into the somewhere else on earth-part of iCloud drive (and just leaving empty file stumps on your computer).