Notes are a lot less focused, and organized. I've got lists of notes that I do not expect ever to cohere into the same story; I just jotted them down to have a note of a Bright Idea.
And then there's notes where I suspect that the stuff involved will cohere somehow, some day, and I even have a fair guess as to which order the events suggested will evolve in -- but I don't have it by the beginning, which is what is needed to start the outline. And sometimes even when I do have a beginning, and an outline, but the Bright Idea doesn't go into the part that exists. Hate to lose a Bright Idea just because it's not the proper time for it.
Which applies even when writing or revising. Scribbled notes are useful. Even when I'm fitting them in the odd corners of an outline, where I hadn't scribbled before, making it hard to read sometimes. And hard to find when I want to scratch it off. (Have to do that. A note to remind me can keep on doing its job. And then I re-read at a canter and find that I put in the same info three times which is overkill.)