A use that the engineers have for the gear pins is tracing a hyraulic leak in the retraction mechanism. If the leak is in the retraction lines, then these will not be pressurised until the aircraft is airborne, gear selected up, and the leak presents itself, albeit with no one present. So install gear pins, and select gear up. (Its nerve wracking!) The up lines are then pressurised, and you can then check for leaks.
Seen it done.
CCCCC......ough