To elaborate upon what adamey has posted, many years ago, vehicles used to just have a wire/multiple wires to each component which required power/ground/signal etc. This scenario could span the entire length of the vehicle, or even longer, considering the eventual routing of a wiring harness.
The addition of more and more electrically and electronically controlled equipment neccessitated either more physical wiring, or a different solution.
CAN-bus, LIN-bus, O-Bus (same as M.O.S.T.) etc. provided an alternative by only requiring power, ground and signal wiring between each control unit placed in the most suitable location. From that location, the neccessary inputs/outputs only require minimal cabling runs to devices, as opposed to the previously employed system.
An example of older technology versus new technology can be illustrated with cruise-control.
Older technology required a separate actuator for the cruise-control, which had to have it's own wiring for power, ground, vehicle speed, cruise on/off/recall switches, throttle position, clutch pedal position, brake pedal position, etc. This actuator was connected, by a cable, to the throttle body on the engine and actually moved the throttle butterfly valve mechanically.
Newer technology already incorporates "drive-by-wire", where the accelerator pedal is no longer mechanically connected to the throttle body butterfly valve. Instead, a pair of potentiometers are housed within the pedal assembly and supply pedal position to the Engine Control Module. From the pedal position value, engine temp value, engine speed value, engine load value, intake mass air value, current vehicle speed value, H02S value, etc. the ECM calculates the most appropriate throttle opening and sends a command. Feedback potentiometers, in the throttle body housing sensor, report current throttle position back to the ECM.
Since all of this information is already being evaluated, re-evaluated and continually adjusted, on the bus, to add cruise control is a trivial matter. No extra wiring is required, only the addition of an extra switch and a quick re-programming function of participating control units.
HTH.