Original writing is just that. Something new. Something that’s never been written before. And, by extension, something that’s never been read before. That’s not to say it’s any good. Original writing can be crap.
So why on earth would we want to use copy and paste? If the writing we’re copying is, indeed, crap we’re just adding to the dung heap. And if it’s any good we’re, at the very least, guilty of being unoriginal.
Whilst they have their uses those two keyboard shortcuts stifle creativity. So use them sparingly. Or, as this article in the Guardian suggests, be more like the actor Tom Hanks and use a typewriter instead.