What allegorical significance does the fact that Napoleon and Snowball disagree during the animals' meetings carry?
I think that the symbolic significance of the pigs' disagreements is that there can really only be one ruler. There can only be one voice of authority. While the revolution sought to eliminate one ruler in the form of Mr. Jones, the intensity of disagreements between Napoleon and Snowball represents how there can really be only one leader and the struggle for this leadership between both is one of the last moments where the idea of "collectivity" in leadership is evident. Once Napoleon runs out Snowball, it is the beginning of the end for the goals of animalism.
From the historical and allegorical point of view, the disagreement between Napoleon and Snowball represents the struggle for power that emerges in Russian history after Lenin has died. For a moment in time, there was considerable disagreement between Stalin and Trotsky, and the fate of leadership was hanging in the balance. The battle between both was waged and the result was that both presented different visions of leadership in the Soviet Union. Similar to Orwell's construction of Napoleon, Stalin was able to use his own power and control, fed by his own paranoia, to run off Trotsky and consolidate his control over the power base of the nation. In this, Orwell's allegory possess political and literary meaning.