[Lindolirian]

I think when Elrond gave in at let Merry and Pippin go with the Fellowship. If they had not gone or Elf-lords in their place, they would not have been captured by the Orcs of Isengard. As Gandalf explains in the Two Towers, their coming was the trickle of water that burst the dam. Saruman was stayed by Rohan and the Ents and Rohan was able to came to the aid of Minas Tirith and save the city. They then formed the Host of the West and made the final diversion to empty Mordor. If Elves had gone in the place of Merry and Pippin, they would have killed all the orcs, Treebeard and the Ents never aroused, Rohan and Gondor destroyed and more orcs still in Mordor to find Frodo and Sam.