I plan to traditionally publish my urban fantasy series The Dead Five once I complete it. I have an editor. But I want to bring her something awesome.
But beyond that is an alpha reader, who reads each chapter as they're complete. These heroes can prevent disaster before it occurs. (Examples: he or she warns the author that the main idea of the novel is falling off course, or that he accidentally changed a city name, etc.)
Alpha readers read chapters.  (Beta readers usually read an entire completed book. They usually lose motivation. But for me, who releases chapters not quick enough, the alpha reader will have time to relax and work on other things)