Snowball and Napoleon have differing points of view about the running of Animal Farm because they have different goals in mind. Snowball is committed to the philosophy of Animalism. Orwell was thinking of an historical figure like Leon Trotsky when he created him as a character. Napoleon is seeking personal power for selfish reasons.
Snowball’s belief is that the windmill would make the lives of the animals better through the generation of electricity. Napoleon doesn’t have any particularly strong reason for opposing the windmill, except that he doesn’t want Snowball to gain power by proposing it and gaining the animals’ support. So, to prevent being eclipsed by Snowball, he has the dogs run him off.
Later Napoleon, realizing that there would be benefits in having windmill, claims that the idea was his all along. The windmill takes years to complete, and never does help make life more comfortable for the animals, although it does serve to enrich Napoleon and the other pigs.