|It's not necessary to
breed Chocobo to win the game, but it's
Side-quest, (probably, the best side
quest out of all the Final Fantasy games,)
plus each special type of Chocobo (Green,
Blue, Black, and Gold) gives you access
to a new cave with special Materia,
including the ultimate Summon Materia.
Green, Black, and Gold Chocobo's also
enable you to reach the Forest of the
Ancients (near Cosmo Canyon) without
defeating the Ultima Weapon.