Archers aren't the best example – it's precisely the ranged units in Quick Battles that allow you to break through without significant losses, because distance isn't a factor there; instead, unit speed matters (the same centaurs can easily defeat slow-moving archers with minimal problems, which is impossible in manual combat). The example with iffrits directly confirms NumOne's words: a close fight, a couple of extra morale losses, and the iffrit is gone, but a replayable quick battle allows you to "reroll the dice" and change the morale outcome. I don't use the 3+ mod, so I wasn't aware of the Q button, but since it exists, what prevents you from starting a quick battle, engaging in combat, and pressing it if you're confident in the outcome? So far, replaying quick battles is a safety net, and no other arguments have been presented (speeding up battles with instant completion should save at least as much time as a replayable quick battle). And saving nerves, concentration, and troops by using a replayable quick battle is an advantage.