Charles Darwin, an inveterate note-taker with special systems of folders and notebooks, wrote in his Introduction to The Descent of Man: "The nature of the following work will be best understood by a brief account of how it came to be written. During many years I collected notes on the origin or descent of man, without any intention of publishing on the subject, but rather with the determination not to publish, as I thought that I should thus only add to the prejudices against my views. It seemed to me sufficient to indicate, in the first edition of my 'Origin of Species,' that by this work "light would be thrown on the origin of man and his history;" and this implies that man must be included with other organic beings in any general conclusion respecting his manner of appearance on this earth. Now the case wears a wholly different aspect." 
One might wonder whether collecting with the "determination not to publish" is different from collecting with an "intention of publishing" or whether there is no significant difference. Darwin could be taken as saying that there is, but I think that would be over-interpreting what he says. He is not focusing on note-taking but on why he is publishing the book at the time in which he published it—in 1871, that is.
Still, he demonstrates—at least indirectly—the value of just collecting notes without a definite purpose. See also Collecting. However, I should also point out that Darwin is collecting his notes with more focus than Klemperer. There would seem to be a continuum between "highly focused" and "completely unfocused," and there might be such "vices" as "too focused" and "too unfocused," with true virtue lying somewhere in the middle. But, as Aristotle, from whom I take this inspiration, pointed out, this cannot be an "absolute mean." It must be a mean relative to the person who takes the notes. It's not a science, but an art, even if it's an art that makes science possible.
1. Quoted in accordance with the Gutenberg e-text of The Descent of Man.