I have documents and photos on my laptop and differrent documents on my stand alone PC.
If you have a network (WiFi or Ethernet cable based), you can
- Share PC folder(s) → Laptop
- Share Laptop folder(s) → PC
as long as both computers are powered on.
But this question got nothing to do with LibreOffice.
You could also use a cloud based service that has a local folder for synchronizing such as Dropbox.
You save a file to the folder and it will be synchronised to the server when computer A is connected to internet. If computer B then connects to internet its local folder will synchronise to the server, picking up the new file written by computer A