Very very slowly working through an excessively large Pocket backlog, and this quote from Drew Magary's How to Write 10,000 Words a Week was a very accurate encapsulation of how I feel about my notebooks:
[...] that notebook is a physical manifestation of a messy room that only I know the order to. Give your thoughts tangible form and then you can exert control over them.
Professionally and personally, I consume massive amounts of information that then proceeds to jiggle about my brain until I can pin my thoughts down and start to make sense of everything. My messy notebooks and journals are enormously helpful in imposing order and I'm always on the lookout for how other people do this too. Don't think I'll ever get to the point of writing 10,000 words a week though!