Type 4 DAISY DTBs provide the richest reading experience, and are currently the most expensive to produce if human voice narration is used (rather than synthetic speech). A full text/audio DAISY book gives the end user the choice as to how the book will be read. It will meet the needs of someone who wants to read a novel from end to end with a DAISY hardware player, without using any of the navigation features or other advanced functionality. At the same time, that same book can be used by a university student reading the book with a DAISY software player; going to specific pages to read the selections for the next tutorial, spelling out proper names for accuracy in essay writing, word searching throughout the book, bookmarking passages for later reference, etc. etc. It's the same DAISY DTB, but it's the end user who determines what functionality to use and how to use it. In an ideal world, all books would be DAISY Type 4 DTBs, but in the real world available resources must be considered.