From Publishers Weekly:
Do you want to sell more books and increase the value of your author brand? Then give some of your e-books away for free.
To many authors, the idea of giving their work away for free is counterintuitive—and possibly abhorrent and sacrilegious. Free devalues your work, right?
Wrong. Free makes your work more valuable. As an author, you are a brand. Readers buy books from authors who have earned their trust. But to earn readers’ trust, you must first earn their awareness. If readers don’t know you, they can’t trust you—your brand carries no value to them. You’re invisible. Even if you’re already a New York Times bestseller, there are millions of potential readers out there who have never heard of you and have never read your stuff.
Free makes it possible to reach new readers who would otherwise never take a chance on you. Free enables readers to sample and discover new authors without financial risk.
According to the 2015 Smashwords Survey, free e-books get 41 times more downloads on average than other e-books. This is the power of free. Free drives sampling and discovery.
Link to the rest at Publishers Weekly