i think that many on this thread are not looking at things in the correct manner...
i say this with all due respect
i was looking at it the same way when i first setup icloud drive...
i want 1 copy in the cloud and a second local copy ..."just in case"
it makes sense because for many years we think about it that way...local copy + backup copy (in cloud or on an external device, etc)
but this is how things are moving (businesses for several years + services like google drive/google docs which are used ubiquitously by high school and college kids)
1. even though the documents folder says icloud drive in your finder...there are local copies on your machine (if you have room)...turn off the internet and you can still edit the document
2. you don't have two visible documents folders...one locally and one in icloud drive...
because icloud drive is managing all the syncing ..,making sure all copies are of the same version...
it matters less where it's stored and more that it is the correct version...
3. the days of each user manually backing up and sending documents to different devices are ending (or have ended)...google, apple, microsoft, amazon all do this for the customers (yes it's not free...but external hard drives were not either...)
yes there are glitches...but there always were when the user did it manually...