You're exactly right Dave !
That's why I'm changing my "strategy".
Until now I had, with me, only a CS sync of some of my most important documents, and, safe at home, an SD clone.
But, as you said, I always needed things that were not with me.
That's why I was asking if I could do a CS -and partial- sync BUT on top of a SD clone, that would have all the rest
But my question was more of a technical one, about "file structures" incompatibilities, or things like that. It seems that, on that particular point, you don't see any problems.
So I take your answer as a "yes"
Thanks again (as always)