Repost because of moderation. (It was the forbidden word.)
You can choose yourself whether to encrypt your books using Digital Rights Management (DRM). On the one hand, it's like locking the door--why leave it wide open? On the other hand, most people are honest, and a non-DRM book can, with the right software, be read on a Nook or Sony or Kobo reader, which a KDP book normally cannot be. It's up to you. But note that no encryption method is safe against dete*rmined thieves.