Its the LOCK PIN I'm referring to here - not the steering disconnect pin.
OK, I'll rephrase the question.
On my Airbus the nose gear LOCK pin acts to prevent undesired movement of the the over-centre lock actuator mechanism.
The over-centre mechanism keeps the gear mechanically locked down. If this over-centre mechanism were to fail during (for example) emergency braking by the tug on pushback - would it result in a gear collapse?
Some say NO - you would have to operate the gear handle to (hydraulically) operate the actuator which breaks the down lock before you could get a retraction, and nobody is likely to do THAT. Hence you don't need a pin.
Others say YES - if you had a hydraulic failure to the actuator coupled with a sudden stop by the tug, it would be possible for the over-centre to break and allow gear collapse.
Having a pin in may be belt and braces - depending on your point of view above - but the only drawback I can see in having it in is that (as 411A said) somebody might forget to remove it some day.
FWIW, we use them, and nobody has had one left in after push-back for at least the last 20 years.