In the books it was just that they would only answer to Isldur’s Heir. They also scared the Corsairs of Umbar away from their ships, but it was an army of Dunadain (along with a few elves, like Elrond’s sons) that actually ran them off permanently, so they could use the ships to bring some of the Gondorians in the south back north to join the main battle.
deleted by creator
Basically, yes.
In the books it was just that they would only answer to Isldur’s Heir. They also scared the Corsairs of Umbar away from their ships, but it was an army of Dunadain (along with a few elves, like Elrond’s sons) that actually ran them off permanently, so they could use the ships to bring some of the Gondorians in the south back north to join the main battle.