Receive a few complimentary copies of your book in the mail (and purchase more at your author's discount price). (kathyide.com)
You will share your views with readers, receive complimentary copies, gain credibility, and may even be invited by a publication to write reviews and articles. (twilighttimesbooks.com)
About used books - if you were given complimentary copies and you gave them out, they can sell those again. (accrispin.blogspot.ru)