Breeding is slightly less significant since you don't have to worry about getting the right natures or abilities. Also, you can't speed up the hatching process with a Pokemon with Magma Armor or Flame Body like you could in D/P/Pt. However, Egg moves and optimal IVs still should be taken into consideration. While not as vital in D/P/Pt, breeding is still desirable for getting good Pokemon in G/S/C.