...runoff from the other place.
Go to your bookshelf, assuming you have one, and pull out a hardcover book. Is the cut edge smooth? Try another until you spot rough-edged pages. Now ask yourself: does this book impress you more than others with trimmed pages, or does it seem defective? Some of Amazon’s customers clearly think think the latter, to judge by a note found on the bookseller’s pages for books with this “feature”.
Text blocks with deckled edges are not a byproduct of the papermaking process, they are a byproduct of roughly chopped...
I just knew the deckle edge was too cute by half! Now waiting for a history of the gatefold paperback.