The 'rules no rules' thing seems to be bubbling on. For anyone who is interested, here:
Half way down the comments is a good one, from Nik. That steering a middle path seems a sensible way to go.
And it is wonderful, no it's WONDERFUL to see a teenager's face light up (as it did when I was teaching at Gateway Tilbury on Saturday), when I say, "All I want is your ideas... write them how you want.. I don't care, not here, not now, about grammar, handwriting, spelling."
But I then said:
"But other people, elsewhere, will care, so at some point you will need to think about that... " and the kid wrote like a demon. He'd learned the difference between letting go just going for it, and academic concentration.
He has learned to splurge creatively, but still knows and accepts that he will need to spell correctly, and write grammatically for his GCSEs.