A rapper can say things about his 'opponent' that, said directly, would result in gunplay.
There is a whole list of Chinese movies that were critical of the Mao and Post-Mao period - at the time - that were political allegories, if you understood the symbolism. The scripts for these movies were so successfully obfuscated that they passed the censors. You can't be me, I'm taken
That which can not be said, can be said if it is space movies with apes and robots.