What benefits does Snowball see for the animals as a result of building the windwmill in Animal Farm?

Snowball thinks that the animals will all have much easier
lives if they are able to build the windmill.  This is why he wants to build it. 
Napoleon disagrees with Snowball -- he thinks that they should just concentrate on
growing food.

Snowball says that building the windmill will
allow the animals to have electricity.  He says this will be good for them because it
will allow them, for example, to have their stalls be warm in winter.  It will also help
them by saving work because there will be some sorts of machines that can run on the
electricity.

You can find more details in Chapter
5.