If a user put a file 'test.py' in the NFS Folder in computer A, only metadata of 'test.py' will be uploaded, say size, file name, time stamp. But the file data like the codes in 'test.py' will not be uploaded. When the user logins with the same account in computer B, the user can see 'test.py' in the NFS Folder, but at that time, there is nothing in 'test.py', except the metadata from the original 'test.py' in A, which tells the user the basic info of 'test.py'. When user double clicks or downloads the 'test.py', the real file data will be uploaded from A to Server and user can download data to B.
When user wants to upload many files which are not very likely to be downloaded in future, this way can save much NFS Folder storage maybe. Because as long as user hasn't downloaded this files, there are only metadata occupied the storage in Dropbox Folder.
Or just take a look at https://help.dropbox.com/installs-integrations/sync-uploads/smart-sync
Is there any free or open source version of that?