Ultimately, leaving a reserve force of a hundred thousand men and possibly one or two Inborn Grandmasters was like holding a plan for contingencies, ensuring that there would still be these hundred thousand men as a fallback if something unexpected happened.
Or if the front-line battle was going poorly, they could be urgently called upon to provide support.
One cannot say that this strategy is entirely wrong.
If one's own side could maintain the advantage, then taking action according to this strategy would indeed be the most prudent, ensuring that one's side remained invincible.
But the question is, does Ning Country really have an absolute advantage over Chu State?
Just looking at the main battlefield of Dongting in Yuzhang Prefecture, the Chu army has 210,000 troops, while Ning Country has 400,000.