Basically, Simplenote has been for anything in progress and Yojimbo was for anything worth keeping. I don’t write in Yojimbo, I store. And for a long time I didn’t store in Simplenote, I just jotted.
But the general idea of taking one tool for storing and the other one for jotting down and drafting text is precisely my way. The question is not whether to use one or the other tool, the question is how to use both of them in a sensible way.