title_body: What are advantages of publishing DRM-protected books for an author? What are advantages of publishing DRM-protected books for an author?
  
  Clearly some authors think that there are advantages of using DRM since they publish DRM-protected books, when they have an option of forgoing DRM.
  
  Please note that I'm looking for hard data, not opinions. 
  
  "DRM reduces piracy" is an opinion. "Switching from non-DRM to DRM raised sales by 30% for author XYZ" is a fact. "A survey of XYZ large sample of users confirmed that only 10% won't buy DRM-protected books, whereas a study ABC showed that there are more than 10% books obtained without paying" is a fact.
  
  "DRM reduces your reading audience" is an opinion. "Combined sales of non-DRM sales points are 120% more than DRM-supporting ones" is a fact.
upvoted_answer: Answering the opposite question, Tor books switched from DRM to non-DRM, and they commented (no figures available) that they saw 
  
  
    no discernible increase in piracy on any of our titles
  
  
  http://www.tor.com/blogs/2013/04/tor-books-uk-drm-free-one-year-later