Uses
The whole concept of the third state (Hi-Z) is to effectively remove the device's influence from the rest of the circuit. If more than one device is electrically connected, putting an output into the Hi-Z state is often used to prevent short circuits, or one device driving high (logical 1) against another device driving low (logical 0).
Three-state buffers can also be used to implement efficient multiplexers, especially those with large numbers of inputs. In particular, they are essential to the operation of a shared electronic bus.
Three-state logic can reduce the number of wires needed to drive a set of LEDs (tristate multiplexing or Charlieplexing).
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