On motor vehicles, and it is not just cars but trucks and trailers using CAN.
The CAN system, operating a speeds up to 1Mbps, is typically used for engine management, braking, steering and other safety systems. It is capable of two way transmission. The CAN bus may also connect with smaller control units known as LINs – Local Interconnect Network – which in turn control individual units. Eg Each door will have a LIN which will control the locking, window, speaker and mirror. Climate control and lighting are other typical LIN applications. LIN is a one way system with operating speeds up to 20Kbps. MOST, as its name suggests is used for media or infotainment systems. Again it is a one way system, using fibre optics, but is capable of a high speed of 24.8Kbps. Speeds of 150 kbps are now coming into use.
As Tony states the biggest problem is connecting other systems to CAN, satnav requires a speed pulse, a tracker may require an ignition or engine run pulse, the steering wheel controls for your phone will be controlled by a LIN and even your alarm will require a CAN connection. The upside is that all these only require a one or two wire connection. The downside is that diagnosis can be very difficult. It must be said that CAN systems are very reliable but whilst dedicated diagnosis systems will tell which sensor, switch or ecu is not working correctly it often falls down on plain wiring faults. As Tony states, a VERY high speed occiliscope is needed.
Given the relatively uncomplicated wiring on a narrowboat, I would do without it.