Denewing also makes your new shelves look better. Because space is at such a premium in most public libraries (although regular weeding could help with that--cough), the New Shelf is the place where we have the best opportunity to showcase what we're buying and catch people's attention. The new shelf should be positioned somewhere where it will catch patrons' eyes and shout (item-wise): HEY, THESE ARE THE COOL, INFORMATIVE, USEFUL THINGS WE ARE BUYING WITH YOUR TAX MONEY.
A "before" shot. Notice how the book on display is squeezed so far over that it's only half visible? That is not ideal. An overcrowded shelf says "sure, put that book back wherever you want, we won't notice."
An "after" shot from one of my sections. Which shelf would you rather peruse?
Leave enough space for one book to be displayed face out and enough space for books coming back to be shelved in the section without creating a space problem for the book on display. New books usually circulate more frequently than denewed books, and sometimes they all come back at once. And, out of consideration for the people (patrons, pages, circ staff, or reference librarians) who will be looking for specific books in the New section, have your display books be from approximately the same call number range as the shelf they are sitting on! A book from the 100s should not be on display in the 900s.
And then there are the opportunities for art . . . all those stickers have to go somewhere, right?
I usually denew every month or so, and the items I'm switching have generally been on the shelf at least nine months. I know from some conversations on Twitter that this is a long time for a lot of libraries, but it seems to work for our collection. Rather than denew on a schedule, I keep an eye on my subject areas (nonfiction only, my collection responsibilities do not extend to hardback fiction) and denew whenever they're looking a little crowded. I may order a lot of books in one subject area one month (e.g., martial arts, for which I recently ordered several titles), which would lead to heavier denewing in that area nine months later. I don't necessarily denew everything I pull off the shelf, either. I might keep a high circulating book on the New Shelf, or one that is seasonally appropriate.
Try to keep in mind that every book that you denew has to have its own shelf space in the regular stacks. For every book in, there should be a book out.
What are your experiences with denewing?