•📄 "Let me just search the PDF" → you get a list of pages, not answers
•🧠 "I'll ask the agent about this book" → it either hallucinates or says it doesn't have the content
•📝 "I'll take notes as I read" → you end up with a 200-line doc you never open again
•Internal documentation — architecture decision records, runbooks, onboarding guides. Fold a whole docs/ folder into one skill and ask it while you code.
•Brand & design systems — voice guidelines, tone-of-voice docs, component principles. Turn a brand book into a skill your team queries instead of skimming a 60-page PDF.
•Research clusters — a stack of papers plus your own notes, merged into a single unified skill and updated as new material lands (see Update / fold-in).
•Specs & standards — RFCs, API contracts, compliance docs you reference but never memorize.
•You use your own copy. Bring a book you bought, docs your company owns, or papers you have the right to read.