The furor a couple years ago over Drake rapping live on Hot 97 while reading lyrics off of his Blackberry exposed a lot of freestyle purists. But more than that, it exposed their naivete. Listen to some of those classic "freestyles" that Biggie or Jay spit at Hot 97 and try to tell yourself those amazing lines came right off the dome. Hell, some of those lyrics ended up on album tracks mere months later, with little or no variation. The truth is, freestyling is its own discipline that only a small percentage of rap's greatest writers excel at. If most great MCs were forced to go completely off the dome, without using any recently composed and memorized bars, they'd probably sound a lot like Lil B, except they wouldn't be spitting "based" freestyles on purpose.
Freestyling is overrated.