Just going through hoops myself to understand this. What I have established is that if at first you migrate the Lightroom Classic CC catalogue using the option in the menu in Lightroom CC, all the photos catalogued previously from Lightroom Classic CC will be uploaded to the cloud as full size originals.
If you then view them in Lightroom mobile (e.g. on a iPad or iPhone), you will see that the local image is a smart preview, with the cloud image is a backup of the original from your computer which you can download to the mobile device if you wish.
Also, I believe if you add photos to the (newly migrated) CC catalogue with the Lightroom CC on your desktop, then the original will be uploaded to the cloud.
Originals do not seem to be uploaded when adding further photos using Lightroom Classic CC as I have just found out by adding some more photos as a test. Only a smart preview goes to the cloud.
So, I don't know the actual answer to your question as to whether the edits (on the smart preview) would be reflected on the desktop version on the original file (I guess they will as long as you have the collection synced). However, when I first tried to edit an image on my iPad which was only available from the cloud as a smart preview, the editing options were not enabled and I am sure that it said the image was not editable! Maybe that was for a different reason than not having direct access to an original image!
However, since uploading the original images to the cloud, I am able to edit the image on my iPad (even if it is only a smart preview on the iPad)!
I am not sure what the intention with regards to cloud file sizes is, but personally I wish to have the original images backed up and available to all devices from the cloud, so from now on I will always use Lightroom CC on my desktop to add photos to the catalogue, and use Lightroom Classic CC to use more powerful editing facilities when at my desktop (because the CC collections will be synced and available on all devices as well as the desktop computer).
The test goes this way:
ZERO images in the Adobe Lr cloud ecosystem
ZERO images in a CLEAN/NEW Lr Classic catalog
Syncing paused in the Lr Classic
Added an 3.3 MB image from a USB drive by way of Lr CC Web
Ejected the USB drive so there is NO possible reference associated to that file.
Image appears in Lr CC desktop, Web and iPhone as a 3.15 MB file (rounding issue maybe)
Turned on syncing in Lr Classic and the image synced.
Using 'Show In Finder' I navigated to that file in a Mobile Downloads.lrdata folder named >
That file, as it sits on my local drive, is consuming 3.3 MB of storage space.
It synced FROM the 'cloud' so it must use that amount of space there.
Pretty much as Steve says:
On Migration from Classic, Full Resolution Photos will be uploaded the the Cloud.
(Without migration Collections synced to the Cloud only upload lower res Smart Previews).
Anything uploaded from LrCC Desktop, Mobile and Web will go to the Cloud as Full Resolution (and if Sync is on in Classic, will download Full Res To there).
You can set LrCC Mobile to just use Smart Previews now but believe LrCC Desktop will download Full Resolution as and when they are needed for some functions. (Both will automatically purge Full Res over time, I believe, just leaving Smart Previews locally to save space).
Hope this helps.
The test of what type of files go where is more easily seen when adding raw images to either catalogue (as in the Lightroom Classic CC catalogue that has previously been migrated to the cloud or via the Lightroom CC desktop app).
I have tried adding raw images via Lightroom Classic to a synchronised collection and then looked at the subject picture on my iPad and when you click the little cloud icon on the top right, it says Local - smart preview and Cloud Backup - smart preview as well.
The previously migrated and then synchronised catalogue pictures will show up as Local - smart preview and Cloud Backup - Original on the iPad.
I think the original as pointed out by selondon will also end in your locally backed up folders managed in the Lr Classic CC catalogue along with any other originals that you may have directly imported into Lr Classic CC. I guess the files which also end up in Mobile Downloads.lrdata would be purged eventually as I was under the impression that is a temporary working area for Lr.
At the risk of rambling on a bit....
If it is of any interest, when I have a larger number of photos where I want the originals to go to the cloud, but want the superior import tools provided by Lr Classic CC, I create a new (temporary) catalogue and import the original photos into there (letting Lr Classic organise the files in my local photos folder as it does so).
I then migrate that catalogue to the cloud with Lr CC on my desktop where it merges the cloud based synchronised catalogues already there storing the originals in the cloud. It seems that whilst you can migrate a catalogue only once, you can migrate any number of catalogues to the cloud where they all merge together creating new albums/collections from the collections specified on import.
I then re-open my original primary Lr Classic CC catalogue where the newly migrated import merges, from the cloud, with my primary catalogue back on my desktop PC.
I have also tried using a memory card adapter to upload originals via Lr CC on my iPad, but there is an issue where if you have RAW+JPEG set on the camera, the RAW files are imported to the iPad, but the associated JPEG (which would normally become the sidecar file for the RAW) is the only file that is uploaded from the cloud (and is declared to be the original, when in fact it the RAW should be the original). This is covered more in depth here: A RAW workflow on the iPad - my initial impressions . The way around this issue is to only shoot RAW (ditching the +JPEG) if you want to import RAW via iPad.
Hopefully some relevant thoughts there!