A headless system is a computer designed to be used from another computer via a network, for when keyboard, screen, and mouse access to a device is inconvenient. Headless access is used for server systems and for building robots. Refer to the following diagram:
The preceding diagram shows a system with a head where a user can sit in front of the device. You would need to take a screen, keyboard, and mouse with your robot—not very mobile. You may be able to attach/detach them as required, but this is also inconvenient and adds bulk. There are systems designed to dock with Raspberry Pis like this and are portable, but when a robot moves, you'd need to disconnect or move with the robot.
I have seen, at some events, a robot with a tiny screen attached and someone using a wireless...