what do I need to see to believe that taking notes (and elaborate on them) is beneficial?
We have one outlier, Luhman, and ... well the entirety 'productivity' web (is this a hipster thing?) who are into it. But are they productive?
In the main, I don't believe that the people doing this are
productive, apart from the mass production of notes.
Most appear to be students; probably the most driven and usually highly performing students anyway. Many appear to have the belief that it will help them learn (though that's not what Luhmann was about); and treat Ahrens' Smart Notes book as their bible even though it conflates his own ideas (developed largely around student note-taking) with those of Luhmann.
Luhmann lived an exraordinarily focused and regular life and was extremely disciplined. His system was perfected to optimise his
productivity, and building on the usual reading and writing work typical of academics. He turned it into a form of painting-by-numbers (so rapid writing at the end). It was a form of academic mass production where the usual academic clay was sorted and then formed into bricks, with an index so that he could quickly find the bricks he wanted whatever he decided he wanted to build in the future.
It's a system I can see working very productively for any academic with his level of discipline (and ability to spot the best clay and craft good bricks).
But not so much for students, and not at all for anyone who doesn't actually have an intention to produce anything at the end of it.
Personally, I've never had that regularity, nor that style of discipline. Neverhteless, I can craft the bricks and the system makes it easy to drop and pick up as desired, with no loss of previously done work. So that's great.
How much effort is it to keep notes?
I don't know. People do appear to be producing prodigious quantities of them.
For me, I don't make a fraction of the notes that most seem to make (though I do have a very good memory, and my own workflow has always been heavily based on that). I have only ever made notes as an essential component of doing something, and even then usually only a fraction of what most seem to believe is required. Even when I was a student, I might make 4 lines of notes, and noticed others with 4 pages or even more; I never could understand what they thought they were going to do with them.
Who is measuring this?
I'd like to believe that everyone doing it will be measuring it for themselves. No way of avoiding bias.
Trying to do matched samples for group work would be fraught with problems, and I don''t think it could be made to work. A longidudinal single-case approach to carefully selected groups might work, but would be expensive to conduct.