Burning the enemy’s fleet is certainly a boon, as it inevitably shakes the morale of the Northern Army. Furthermore, torching the grain supplies at their northern encampment serves as a powerful deterrent. After all, what kind of war can you wage without food? You wouldn't even have the strength to march.
However, there is a downside: it steels their resolve. With no path for retreat, they are forced into a "fight to the death" scenario—they must push forward, and without food, they have no choice but to seize the Southern Kingdom’s own supplies.
On the whole, however, the benefits outweigh the costs.
Chapter 278