There are distinct advantages to encouraging students to learn the rules by breaking them. Deliberately doing it wrong removes the threat of failure. Finally, this method, as I use it, helps train students to edit their own work and the work of others. They learn, in a playful way rather than punitive way, to spot bad writing and correct it. There are also psychological advantages to this approach.
Some students revolt outright.
Some resist passively. Some quietly subvert you in class. Others subvert themselves by failing at things they could perfectly well do. After all, it's something anyone can do well. And when that capricious voice comes out, along with it comes some of the creative energy that is so often locked behind the student's fear of making a mistake.