I find GF's useful throughout the game for bosses and at the beginning of the game for random fights. But by the time you have the best GF's you can junction things like Auto-Haste, Initiative, and Stat-Atk-J, you can make mincemeat of most random enemies without resorting to summoning GF's.

Add the controller set to Memory and you can use brute force to pound away at the enemies until they're dead. At least that's my style of play.