I wouldnt say Biggies freestyled his songs, maybe some but that shits way too lyrical to freestyle. Ive heard him freestyle and hes muthafuckin dope, but his written shit was golden.
I know ther are like 100 different definitions of what a freestyle is. But I don't think Big freestyled on his albums. BIG wrote in his head. Read that Shorty B interview. He talks about when he got down with BIG in the studio.