I have seen several discussions and articles about LR Mobile, syncing, using iPads and limitations from Apple etc, and comments that LR mobile is not a backup solution.
However, I went on a 6 week holiday and took about 100GB worth of photos. I used the iPad successfully while away to upload, rate, edit and publish to social media etc.
Each day, I regularly and laboriously went through the process of importing the images into Apple's Photos app, then adding photos to the LR Mobile collections that I set up for each new place we visited. After a while, the iPad was running out of storage, and so there was then a horrendous workflow involving importing to Photos, adding to the LRMob collections, deleting last Photos import, and then clearing the iPad Photos "deleted folder" to really remove them. Sometimes towards the end of the trip I had to do this in batches as the iPad storage was seriously in short supply. I did edits on the LRMob images, and rated the photos (the normal LRMob expected workflow). Publishing to Facebook went pretty well, with the odd glitch where LR Mobsimply failed to do anythig after poricessing the images for publication. And it has a serious flaw in that it seems to publish photos in a random sequence, totally unrelated to the order of photos deliberately selected in sequence for publishing (and not even seemingly related to capture time!!!). This is not a good "feature"....
Generally, however, so far so good.
What I cannot work out from the tutorials, and other limited web info, is what to do next. I know the images are in the cloud (they sync'd all holiday), but I suspect they are limited resolution ones, so not the full NEF I have stored on the iPad. I'm pretty sure the NEF is intact on the iPad, as the device reports nearly 90GB of photos used in LR Mobile.
Ideally, I would like synchronisation to now take all of those FULL NEF images and seamlessly place them on my LR desktop now I am home and the mac is fired up. I don't think it will, and suspect that all that happens is that editing / rating info is transferred there, together with a "lightweight" image, under the "From Lr mobile" collection. However, that doesn't seem to be happening. The activity indicator says that it is "Syncing 3,163 photos", but if I check preferences to see what progress is made, it all seems to be stalled. (Actually 3,609 pending, and like that for over an hour. Go figure..... I don't understand why the 2 numbers are different, but they are!)
I wonder whether the issue is that LR mobile syncing needs the original images to be located in a LR Desktop collection before syncing can happen? If so, that is a real pain, as I will then need to painstakingly recreate the collections (Same name, all photos in equivalent places) - what a waste of time!
I hope I have got this wrong.
It would be very useful to have a definitive guide from Adobe experts on using LR Mobile for travel photos to edit and sync with LR desktop - with the basic fact that the initial process starts on the LR Mobile, NOT the desktop version. And given that tablets are a massive benefit in travel over a laptop - please use the tablet as the "input device"...
In the meantime until Adobe can address this, any help and advice is really welcome from the community!
Update. This doesn't address the main question, but at least I have managed to start the sync process. For some reason, even though a destination folder was identified in the Preferences, Lightroom Mobile tab, and was selected, using that dialogue to select the folder again triggered the sync to start. I have no idea why that was the case, or whether this is a bug or feature....
If sync is turned on in Lr Desktop then high res files uploaded from LrM will sync to the cloud then back down to the designated folder in LrD still at the original resolution.
Once synced to the cloud LrM will manage its own space optimising as required. You can always clear cache that may create space also.