"New items were entered in a miscellany in no particular order, in any available space, whereas commonplace books were more organized, with entries entered under specific headings to aid subsequent retrieval. In 1512, Erasmus of Rotterdam suggested detailed guidelines for keepers of commonplace books, suggesting that they should file noteworthy quotations under various headings for content, structure, or style. [...] Once squirreled away, interesting facts or turns of phrase could be easily retrieved by the book's owner when composing his or her own poems, letters, or speeches. A commonplace book or miscellany also provided a record showing how its owner's interests or passions changed over time. The custom of keeping commonplace books in this way grew out of the earlier tradition among churchmen of collecting florilegia (literally, 'gatherings of flowers'), which were compilations of excerpts from Christian and classical sources to be drawn upon when composing a sermon."
Tom Standage, Social Media: The First 2000 Years