Jon spent most of the night awake, thinking if he should use his dragons in the upcoming battle and, if so, how. In the end, he concluded that he had to get Ramsay to commit most, if not all, of his forces, before throwing the dragons in. They wouldn't cause much damage, but maybe they could cause mayhem and break the enemy lines with fear, if not with fire. If he called upon them too early, Bolton would simply retreat to Winterfell and turtle up.