News to me, but people watch other people play video games. When they do, you can see the game they are playing, and then there is a screen within a screen that shows them while they are playing.

Imagine a celebrity playing a video game and a host of people watching. What happens if they start flashing interactive links for merchandise from the celebrity. Or links to other games. Or points to use for their own play. Or PDFs with tips and tricks. Or whatever they are trying to sell to a crowd of motivated and highly impulsive buyers.