Will Ferrell shares how he decided it was time to leave SNL and take a risk by filming "Elf.""I had been at SNL for seven years and you have to leave at some point. Unless you're Kenan, he's still there and he's literally the only one who could pull it off. Short of Kenan, you're always thinking about when's a good moment to fly the coop.""It felt like I had enough momentum but it's not like I had a stack of scripts waiting for me. We were developing this movie about a human raised by elves at t