There are many privileges that the pigs gain. At first, it is small things like food. Later the privileges are far greater. In the beginning of the book, the pigs take milk, and they are able to justify it through rhetoric. Here is what Squealer says:
‘Comrades!’ he cried. ‘You do not imagine, I hope, that we pigs are doing this in a spirit of selfishness and privilege? Many of us actually dislike milk and apples. I dislike them myself. Our sole object in taking these things is to preserve our health. Milk and apples (this has been proved by Science, comrades) contain substances absolutely necessary to the well-being of a pig. We pigs are brainworkers. The whole management and organisation of this farm depend on us. Day and night we are watching over your welfare. It is for your sake that we drink that milk and eat those apples. Do you know what would happen if we pigs failed in our duty? Jones would come back! Yes, Jones would come back! Surely, comrades,’ cried Squealer almost pleadingly, skipping from side to side and whisking his tail, ‘surely there is no one among you who wants to see Jones come back?’
Later, the pigs gain other privileges. For example, the pigs change the fourth commandment so that they can sleep in a bed.
‘It says, ’No animal shall sleep in a bed with sheets,” she announced finally. Curiously enough, Clover had not remembered that the Fourth Commandment mentioned sheets; but as it was there on the wall, it must have done so. And Squealer, who happened to be passing at this moment, attended by two or three dogs, was able to put the whole matter in its proper perspective.
Finally, Napoleon turns into a man. This shows that by the end the pigs gain everything.