My understanding, and someone please correct me if it is wrong, is the it is a matter of what is actually sync'd. If you have a RAW file on your desktop, the only thing that is sent to the cloud, or to your iPhone or iPad, is a "smart preview", or a "full resolution" preview (somewhat larger) if you request it, but not the raw file itself. Conversely, if you take, or copy, a raw photo on your phone, then the raw file is sent to the cloud, then to the desktop, but not to the iPad (only the smart preview). On Lr Web, the raw files just pass thru, the editable smart previews stay. On your phone, once things are sync'd, you can delete the raw from the camera roll, but but your collection remains, and you have full editing capabilities. You can then delete the originals from the camera roll, but I would be VERY sure that everything is on the desktop before you do so.
... View more