First thing that comes to mind is the play, "Tartuffee", which mocked hypocritical priests who preached the holy bible but sinned in private and were secretly corrupt. Controversal subjects, like this, could have profound impacts on society and bring attention to these taboo subjects. Although at the time of release they didn't preform too often, it's now recognized as a major work and contains valid criticism. This isn't to say there isn't limitation over what should be talked about, but at the very least it's impossible to ignore the positive impact it had on society as well.
Answer:
The benefits of controversial theatre productions are:
Innovation, the controversial experiences are usually kinda unique and experiment with different topics that are not addressed a lot in the common scene.
Different viewpoints to the mean population, a lot of times the mean population is maybe ignorant about some topics, and you can see lots of cases in the near history, like ignorance (and hate) to different races, beliefs, and sexual orientations. Usually, a controversial production can take one of these topics and work with it, then when the audience sees the play maybe they can learn something about these "controversial" topics.
Different emotions: Usually controversial art does not necessarily try to be beautiful or sad, they may point to other emotions, like fear, disgust oppression, etc, and sometimes is refreshing to feel different emotions when you see a play
Are there limits to what should be staged? well, yes, of course, illegal things should not be done, but other than that no, there are no limits in the art.
