During the conflict about the first windmill, it is clear that Napoleon only wants to shut off support for Snowball so he can continue his movement towards dictatorship. Because of this, he has no real plan, just the blind support of the sheep and vague promises of plenty in the future. While Snowball's vision is of machine-assisted farm life, with a reduced need for manual labor, Napoleon needs the animals to be overworked so they can't think about rebelling against him as they did against Farmer Jones.
...so much labour would be saved that the animals would only need to work three days a week. Napoleon... argued that the great need of the moment was to increase food production, and that if they wasted time on the windmill they would all starve to death. The animals formed themselves into two factions under the slogan, 'Vote for Snowball and the three-day week' and 'Vote for Napoleon and the full manger.'
(Orwell, Animal Farm, msxnet.org)
The slogans themselves betray the real attitudes of the two pigs. Snowball wants to use human technology to create a farm on which the animals can subsist for themselves, without ever needing to interact with humans, and so he points out the real results of building the windmill. Napoleon knows that Snowball's plan makes sense, and so his slogan is simply the empty promise of more food if the animals work the farm itself instead of building the windmill. Napoleon's slogan has nothing behind it; his words are empty, just as Snowball's are substantive.
Snowball's slogan: "Vote for Snowball and the three-day week"
Napoleon's slogan: "Vote for Napoleon and the full manger."