By pelting the attacking enemy with tiles, brick and other objects, these impromptu peltasts could take a heavy toll during urban fighting (the most famous casualty of such amateur troops was the great Pyrrhus, brought down by a woman bashing his head with a tile).
The sarissa-wielding phalanxes were vital in every early battle, including the pivotal battle of Gaugamela where the Persian king's scythe chariots were utterly destroyed by the phalanx, supported by the combined use of companion cavalry and peltasts (javelineers).