It's a brief stage show where the villians come down to spots around the castle for the most lightning fast of pictures. We did it because, after 20 years of going to Disney, I hadn't yet seen Malificent who is my fav Disney villian.
In all honesty, the stage show is meh, neither exceptional or terrible, though I'm not into the stage shows at all, and it was only pure dumb luck that we got to see Malificent. We were on the exact side of the stage she came down on only feet away from the line as it formed, but even then, we ended up about 10 people back in line. It took only seconds for each villian to have a line of 50-100+ people (some villians had shorter lines, only 5 or so in line to see them, others like Malificent and the Evil Queen had much longer), and honestly if you're not into the pictures or meet-and-greets, you could probably skip it in favor of making sure you had good seats for the parade which, IMHO, was not to be missed.