Cough has hit on one of the main uses for the pins also on some aircraft when the hydrulic system is totaly de-pressuised to check the precharge PX in the accumulators this can miss position shuttle valves and when the system is re-pressuised strange things happen as the pressure gets into places it should not.
On the BAe 1-11 if you dont put the nose gear lock in after checking the stby steering acc px you run the risk of retracting the nose gear when the hydrulic pressure is re applyed.