As in, if you SSH into a remote machine, Fig can offer completions for that remote machine. Same thing if you are running an interactive terminal for a docker container.
This seems like black magic, but it really does raise a lot of questions about the telemetry issue. It's one thing to potentially leak information from your own machine, but leaking data from remote servers you ssh into requires a whole 'nother level of assurity around privacy.
That said, it's pretty attractive because it's much harder to make a case to install fish on remote servers.
This image may help clarify: https://fig.io/images/slideshow/screenshots/ssh.png