Snowball provides them with a scapegoat. When anything goes wrong on the farm, they can claim it was Snowball's doing or influence. They can pretend that they saw his tracks, or smelled his scent, near the area of any negative incident. Also, in order to stir up fear and animosity amongst the other animals, they can spread rumors about Snowball's involvement in anti-Animal Farm activities, or his cooperation with the neighboring farmers. Once they drive him off, they can use him more than they ever could have used him while he lived on the farm.