If L/G System is Pressurised Hydraulically.The Disconnect Pin Isolates the Pressure & return lines to the Steering Actuators & helps create a runaround between the Actuators to enable the NLG to move freely with the Tow Bar.
Engines can be started on Pushback saving Vital time.
The Steering pin with Red streamer is removed after the Tow bar is disconnected & shown to the Pilot at Taxi clearence by Ground crew.
regds
MEL