What does it mean that the smallest useful unit?

The smallest useful unit is the level of decomposition where each piece carries independent meaning — small enough to be precise, large enough to be self-contained.

Example: You take notes during a strategy meeting. One note reads: 'We need to rethink our approach to customer onboarding, retention metrics, and pricing tiers.' That's three ideas fused into one sentence. Split it into three separate notes — each about one concern — and suddenly each note can link to different projects, attract different evidence, and evolve on its own schedule. The compound note was smaller than a transcript but still too big. The three atomic notes are the smallest useful units.

Try this: Take your most recent set of meeting notes or reading highlights. Find one entry that contains more than one idea. Split it into the smallest pieces that still make sense on their own — where each piece could stand as a complete thought without needing the others for context. If you split too far and a piece becomes meaningless without its neighbor, merge them back. You've just calibrated your personal granularity threshold.