Print On Demand (POD) copies are printed digitally, page by page, rather than on traditional offset printing presses, generally in small batches (or even as a single copy). POD works out more expensive per unit than traditional large print-runs, but it is fast and flexible. At Practical Inspiration we print a traditional printrun of each title, and copies are shipped direct from the printer not only to the author (our authors receive 100 copies as part of our publishing package), but also to our warehouses in the UK, US and Australia. This is important because bookshops won't order copies of books that are ONLY available POD to stock on their shelves, as they can't return them if they don't sell: they'll only order them in if a customer specifically requests the book and pays up front for it. (NB we pay for the stock that we warehouse, not the author: as each copy is sold, the cost of manufacture is deducted to calculate the net revenue on which the author's revenue is based.)
However POD is useful when we suddenly and unexpectedly run out of stock and need to fulfil orders quickly, or if small quantities of customised stock is required, eg with a client's logo on the title page. It also allows us to publish more sustainably, avoiding overstocks and printing locally to replenish stock in an overseas warehouse, thereby avoiding unnecessary shipping.
POD quality is excellent, although you may notice that the spine of your book is sightly thinner when it has been produced this way, as the paper stocks used are slightly different.
Because we use both traditional and POD printing interchangeably, we avoid special finishes such as spot laminate, foil embossing, or jackets with flaps, which can't be produced POD. (Special finishes are also bad for the environment, as the resulting books can't be recycled, which is another reason to avoid them!)