Will Self writes in the TLS about the dangers of self-plagiarism.

As to borrowing one’s own words from oneself, rather than from one’s subjects – surely this cannot be accorded a great crime? My late friend the journalist and critic Elizabeth Young once said to me that what we jobbing journalists do (by which I mean those of us who have plied our trade being prepared to write about more or less anything, for just about anyone, and to any length) is to provide our readers with a form of “mental bubble wrap” that they can sit at home popping with their psychic digits. It’s a fair point, but it prompts the question: is it short-changing readers to offer them some re-inflated bubble wrap they just might have popped before?
It’s surely axiomatic that the greater the prolificacy of the writer, the greater his or her capacity for self-plagiarism. This has to be one of the principal reasons why we admire such productivity rather less than classical economics implies we should; another is embodied in Mark Twain’s witty cynicism: “I didn’t have time to write a short letter, so I wrote a long one instead”. At certain times during my freelance career, I have been filing anything up to a quarter of a million words a year (I include books in the estimate), so is it any wonder if I’ve repeated myself – and sometimes knowingly? For years, my rubric for self-plagiarism was this: in my fiction I tried to create new conceptual space, coin fresh metaphors, bend and warp language in surprising ways – the books had fewer readers than the newspaper and magazine work, so it seemed perfectly legitimate to transplant images, riffs and coinages from this sequestered word-garden into the brighter but more ephemeral light of the daily and weekly press.