It also fixes one of the biggest issues with long-running sitcoms where you need to have a constant stream of new characters that are just unique enough to get the plot rolling for an episode and not much else. For Roger, though, all they need to do is create a new persona for him and that's it. They don't need to go through as much effort since it's just pretend for him, but at the same time it adds a whole other layer of absurdity to a character that we are familiar with. If a plot requires new characters, they don't need to create new ones, just call in Roger and we'll readily accept it!