Why are Brad Paisley, Ludacris and Kesha subjecting themselves to 'Rising Star'?

As we know by now, serving as a judge/coach/mentor on a reality singing competition show can go really well: Just ask Jennifer Lopez, Christina Aguilera and Blake Shelton, who have all received boosts in their careers. But it can just as easily turn into a nightmare, especially if the chemistry isn't all there on the panel: Mariah Carey and Nicki Minaj can surely tell you some stories. Nicole Scherzinger is probably a bit scarred as well.