There is the well known belief that everybody has one novel inside them waiting to be written, whether this is true or not there are certainly plenty of people who have written their novel and want to get it published. Simply because you have achieved the impressive feat of writing a novel doesn’t mean that you are then guaranteed to have it accepted by a publisher and printed. It is for this reason that some authors decide it is in their best interests to publish their work themselves if they can afford to do so.
Not everybody who writes a novel or collection of poetry then goes on to have it published to critical acclaim immediately and they may find that it is rejected by a number of publishers. Publishing companies receive more manuscripts than they are able to publish and so there has to be a process by which they are able to find the works which are most suitable for printing and are most likely to sell in the shops. If an author has been rejected by publishing companies and can afford to do so, they might decide to fund the publishing themselves with the hope that they will make their money back through sales of the book. In these situations it makes financial sense to use a printing company who offer a print on demand service. Using a print on demand service means that a small number of the books can be printed and then once they have been sold more can be printed as and when they are needed. This method can work out much better than having thousands of copies printing and then discovering that only a limited number of people actually want to buy your book.
It is not only aspiring authors of novels or poets who want to publish their own work as there are lots of people who may want to have some published or printed for a variety of reasons. If a student is particularly proud of their dissertation and want to send copies to people they know or academic institutions which may be interested they might use a print on demand service to publish a specific number of copies to send out. Similarly if somebody makes a very moving or memorable speech at a wedding or specific event and people request to have copies of it, it can make sense to pay to have a certain number printed by a professional printing company.
Self-publishing can often be a means of getting your work published and noticed when other options are not available. If a publisher rejects your work it doesn’t mean you should necessarily give up writing; you may need to refine your style or keep writing until you find a style which works best for you. If you are convinced that your work is worthy of being published and you want to see it happen then you might find that funding the publishing yourself is the best way to get the results you want.