All I would add to what has been said is that it indicates that raw power in the hands of someone who is willing to use it (for his own benefit/agenda) will usually triumph over the intellectual leader who depends on ideas. A key idea starts a revolution (The Old Major), but the revolution often falls out of the hands of the idea people and into the hands of the power people. It's one of the most amazing things about the American Revolution that it never happened here; it's one of the only countries where, if you lose an election, you just go home and start over. If you want to look at what can go wrong after a revolution if it falls into the hands of the wrong people (other than the Russian Revolution, that is), take a look at the French Revolution.
Snowball is a pretty popular leader on Animal Farm. (In terms of the book's allegorical references, he represents Leon Trotsky.) Snowball devises several plans for the future of Animal Farm, most notably his plans for the windmill, which sparks a debate amongst the animals. Just as Snowball begins to gain too much popularity, Napoleon has him exiled from the farm, never to be seen again. Typically, Snowball is seen as the better of the two possible leaders (himself and Napoleon, who represents Joseph Stalin). Howver, both pigs step up to try to seize power once Mr. Jones is overthrown, and both do abuse power fairly early on. For example, they partake in the eating of the windfall apples by the pigs, justifying it because they are the brain workers of the farm and need better food than the other animals.