Making Snowball the scapegoat, the reason for all the problems and challenges faced by the animals as the struggle to establish and maintain Animal Farm, gave Napoleon a rallying point to unite the animals in a common viewpoint. If everyone seemed to agree that Snowball had been the reason for any misfortune or difficulty, then noone would dare to be different and suggest that there might be someone else responsible - such as Napoleon. "Whenever anything went wrong it became usual to attribute it to Snowball."
As Napoleon consolidated his control and expanded his complete domination, the other animals came to understand, or at least accept, that it was easier and safer to blame Snowball instead of challenging Napoleon. Certainly, Snowball's exit from Animal Farm was designed to strike fear and obedience into the onlookers.
At this there was a terrible baying sound outside, and nine enormous dogs wearing brass-studded collars came bounding into the barn. They dashed straight for Snowball, who only sprang from his place just in time to escape their snapping jaws.