Thanks for your reply, Tony. But I'm still a bit confused about how to do this in the free version. The message you cited says "everything starts out as placeholders, by default." That wasn't the case for my situation in which I made copies of various folders in the odrive folder. The odrive folder automatically uploaded everything I copied there to ACD and left the odrive folders using full 40 GB of storage. No placeholders survived.
The message you cited responded to a question about unsyncing in the free version and it outlined three methods:
1) Unsync [but apparently that can't be done in the free version]
2) Unlink and relink a source [Could you explain how to do that? None of the odrive items exposed by right clicking an odrive folder say anything about unlinking]
3) Deauthorize the odrive client [This one I understand]
Browsing the forum I have seen several references to the "What is free vs paid" post which states the free version includes "Full, automatic, bi-directional sync with placeholders." I'm just not seeing how to get those placeholders except maybe by option 3 in your reply above.