Because reading, annotating/note taking, and occasional outlining and writing can be broken down into small, concrete building blocks, each part of the process can be done separately and discretely with relatively easy ability to shift from one part of the process to another.

Importantly, one can be working on multiple different high level projects (content production: writing, audio, video, etc.) simultaneously in a way which doesn't break the flow of one's immediate reading. While a particular note within a piece may not come to fruition within a current imagined project, it may spark an idea for a future as yet unimagined project.

Aside: It would seem that Ryan Holiday's descriptions of his process are discrete with respect to each individual project. He's never mentioned using or reusing notes from past projects for current or future projects. He's even gone to the level that he creates custom note cards for his current project which have a title pre-printed on them.

Does this pre-titling help to provide him with more singular focus for his specific workflow? Some who may be prone to being side-tracked or with specific ADHD issues may need or be helped by these visual and workflow cues to stay on task, and as a result be helped by them. For others it may hinder their workflows and creativity.

This process may be different for beginning students or single project writers versus career writers (academics, journalists, fiction and non-fiction writers).

As a concrete example of the above, I personally made a note here about Darwin and Lamarck for a separate interest in evolution which falls outside of my immediate area of interest with respect to note taking and writing output.

Apparently sharing/comparing notes was reasonable advice in 1910 including the idea of in-class signals for splitting up note taking amongst multiple people.

Compare this to shared notes (Google Docs, Etherpad, etc.) in modern context with multiple people doing simultaneous notes.