Although digital media costs less to maintain, there are some good reasons to keep a small inventory of physical books. For one thing, if you've seen the reviewer site listings in our book, you'll notice many of them prefer a physical review copy. Some will even outright refuse e-books. You could just focus on reviewers who accept e-books, but then you could be missing out on the possibility of getting a great review from a book reviewer who would otherwise love your work! Having hard copies also comes in handy if you plan to do a giveaway. People will be more interested in getting a physical book as a prize, rather than an e-book. Of course, you can also keep stock to sell your books at special events or book fairs and even sell your books one-on-one to interested parties. These are all situations where having a copy of your book is extremely valuable.
So how do you go about keeping an inventory? One answer is Print-On-Demand. Sites like CreateSpace can fill small orders and ship the books directly to you. You'll get exactly the number of books you request and no more, minimizing expenses. If you've published through CreateSpace, Lightning Source, or any other self-publishing press, you can use Print-On-Demand to get your stock in a manageable size. However, you also have the option of using a local printing service. If you have printers in your area who specialize in books, you can place an order in-person and make sure that your specific requirements for your book are met. Finding a reliable printing service can be a great asset not only for your current book, but also any future publications you might make, since you'll have a service you can return to again and again whenever you need to do another short print run.
Choosing the amount of inventory you carry and who you want to order copies from does take a bit of research and common sense, but it's well worth your time to consider the possibilities.