Yeah, for one unit vs. unit battle, the odds won't change even if you reload. But let's say you're attacking with a stack of 5 different units, and each of them have a 20% chance to win the same fight. For simplicity's sake, we'll assume that if you try the battle with all 5 units individually by reloading five times, only one of them will win. Then, because you've reloaded and the odds never change, you know that that unit can win the battle, so you use him only, and you easily win a battle that would have required you to sacrifice maybe 1 or 2 units to win. Understand?
In defense of this trick, I read someone on the forums here say that "oh, it's ok to use it if everyone else uses it," but the point I'm try to make is that that's just untrue, because if everyone uses this trick, offense becomes a much more viable option than defense, thus changing the game mechanics. So it's not just a question of opting into a play style; it's basically breaking the game. Cheating, pure and simple. Plus, who the hell wants to reload a save 5-10 times or more for one turn when at war? I for one use a laptop that firmly qualifies as hella slow, so on those grounds alone I'd be opposed to it.