I thought FF3j's battles were fast enough even without the turbo button, so I didn't use it. I did use it in FF2 NES's battles since they were very slow, especially if you use a spell to target all 4 characters or 8 enemies (hits them one by one, then shows a damage box and disintegrates the target if it was killed). I don't see how the turbo button would make FF3j any easier, though, since the battles are turn-based, not ATB. It only makes them go faster.