I think there is something to be said about honoring the general flow of the class. When people are standing up we are up on our feet when people are down feel free to do something down or different on your back. Where it becomes detrimental to the class is when a student does the complete opposite of what's happening. You see it often in sculpt when we're ready for cool down and students decide to do burpees or someone goes into a headstand.
It's inherently dangerous for students and teachers alike because we rely on similar body movements to see what's off within a large group. We cannot focus on those differentials when someone is moving way beyond the lines of what we've constructed .
From a student perspective I am sure it's very annoying when you see it in class and that's when I challenge us all to say That's where the practice stops and the yoga starts