Idea for a product: Stealth KVM (over IP) - The title says it all
A more mundane use can be having a non-technical on-site person plug it into their local server/machine to get a support even when there's a problem with the OS and it won't come up.
Having full "physical" access to Keyboard/Video/Mouse (and network) can be a huge help, especially now that traveling is limited in many areas of the world.
As for the "Stealthy" uses - i'm sure more than a few can be easily found 🙂