IMO we don't really need Cassano, I can't deny that he has amazing skills and would be a great addition to any team. But we don't really need him.
We already have 2 players that fit into the same category: Del Piero and Mutu. Cassano is better than Del Piero, but Mutu is better.
And I wouldn't replace Del Piero with Cassano, why? Because of their mentality. Del Piero is always trying to prove himself, and even when he was benched by Capello, he didn't complain much (Although the fans and media did).
On the other hand, Cassano is a big risk to take. Capello can control him, but what happens after he leaves? Would he have learned to behave himself by then? I'd take that risk if Juve were short on forwards, but right now we have more than enough.