So perhaps the danger you're thinking of is the opportunity cost of spending time writing something that goes nowhere? That's sensible if you're already prone to writing lots of things and need a filter for what not to write. If you're like me, though, you don't write enough, and thoughts that you might productively pursue with the assistance of a keyboard/screen don't get pursued if you're always thinking about who'd want to read it before writing, or thinking excessively about making it "sound right" instead of just getting the ideas out in a form that is clear to yourself. So the relevant opportunity cost for someone like that is ideas that you don't give expression to or that you fail to discover, perhaps to your surprise, that some people will respond to favorably to your writing. In this sense, I think the principle is pretty useful, at least for me. If after writing it you think people won't like it, you could publish under a pseudonym, or just move on to writing the next thing.