The Purpose of Beta Reading
I use Beta Reading for the purpose of Developmental Editing, which is the process of finding issues within the story: plot, character, setting, etc. It isn't necessary to catch all the grammatical or punctuation errors at this point because I will be sending it to the editor after we're done. Beta Readers are fabulous for helping smooth out the story itself, chapter by chapter.
FOR EXAMPLE: When editing Wingbound...
1. I accidentally changed a character's eye color from the beginning to the end.
2. There was a "prop" issue where a saddle was never removed from the dragon in one scene and was gone in the next.
3. Another Beta Reader helped me see one of the characters needed to be described earlier.
4. There was a scene that had NOTHING happening, so a Beta suggested I shorten it and drop the boring stuff.
Let's find those pesky holes!