What is the advantage of configuring a layer in the plugin "QField Sync" for "offline editing" vs just leave it at "copy", do the field work and then copy the edited data from the tablet to the original project folder on my PC? As is understand it, there is no error handling for layers marked for "offline editing" ..so why bother?
Offline editing is useful for collaborative editing. While using it offline, it will create a log of changes (added, deleted and updated features) and reapply those changes on sync time to the main data source (db or file).
Copying files works perfectly fine if it is just a single person working on the field.
You might be interested in watching this presentation about different strategies. Offline editing is explained starting at the start of the part about Nadja, copying is explained with the use case Maya