Doug Little is a jazz musician and a member of The Motion Poets, an improvisational jazz band. If everything is free, it is not going to be focused. You have to have some rules.
Improvisation comes only after long practice makes the song form second nature to the musician.
Then I am comfortable improvising over the song form. The better you get the simpler the rules seem. At the highest level the musician does not think about the form but just performs. The improvisation over a song form is never duplicated. The whole idea of jazz is that once you have played it, it is gone.