Let's say I have a new installation of Lightroom, and I don't have the options ticked for keeping all smart previews or originals on my Mac. However, my library already exists on the Adobe cloud because it's been set up on another Mac. Let's say it's a really large library, like 500GB. So the new installation starts downloading and setting up the library. Does it have to download the whole 500GB? It shouldn't need the originals, because I haven't asked for them to be stored. Does it even create smart previews in this process if I haven't asked for them to be stored locally?
It also seems to me that smart previews could be stored in the cloud so they don't have to be created locally. Are they? The help for the setting "store a copy of all smart previews locally" says "Select to always keep all the Smart Previews on your computer’s hard drive, in addition to backing them up to the cloud." This makes it sound as if smart previews are kept in the cloud, so even if LR wanted to create a cache of smart previews, it could download those, rather than creating them from a downloaded original.
So should the initial load take ages or be (relatively) quick?