What ?Sync the client state over several installations/machines, especially the applied user settings and mods.
Why ?I play Factorio on different on my gaming PC and on my laptop. When I switch from one machine to the other, I have to update the client to the state I want which means in my case I must adjust the graphics settings (brightness to -15 and color Filter to Deuteranopia). Also, depending on the map, I must search and install all the necessary Mods I need.
Ideally, when I switch from one machine to the other, I can just continue where I left and the game client takes care of sync process.