Flava Flav is a fascinating case study in the psychology of fans. He's credited with popularizing the role of the hype man in rap groups, yet often gets unfairly hated on for this role because it appears "simple" and "pointless".
This is incorrect. Flava Flav had a profound effect on improving Public Enemy.
He's offering a proper introduction to the rest of the group, thus increasing the effectiveness of their message. Take a speech making class and you'll realize the importance of having a proper introduction. It's hard to start a dynamic, riveting presentation when you're introduced by Ben Stein on valium. First impressions matter and shape the rest of the all future interactions. You want the audience primed for you.
Mr. Flav was like an opening act that always brought the energy of the crowd up in a manner that fits what Public Enemy envisioned.
So people were primed to have an awesome concert experience because Flava Flav got them riled up and in a good mood. Awesome. But this gets even more interesting. It's well known that Public Enemy was a very political act and, even though Flav seemingly was less involved in this aspect than Chuck D or Professor Griff, he still served this aspect of the band. People in positive moods are significantly more persuaded by a message and less likely to critically process the message in depth.
Flava Flav gave Public Enemy's message the extra persuasive strength it needed to really resonate with their fans.
So this part is important. Before you get off stage, always make sure to hype the crowd up for the next act. Do them a favor, and when it gets returned to you, be grateful. If you have to, go up and ask them to do this before your set. You've got another band bringing you some Flava.
All the bands win when the crowd is in a crazy-excited mood.