I agree with Hazel's summary, except that I would say a reviewer does
not necessarily need technical knowledge. Newbies can often spot
problems that knowledgeable readers won't notice, for example
regarding whether explanations are easy to understand or another
illustration would be helpful or the terms used in the text don't
match the terms in the illustrations.
Anyone can follow the instructions and look at the pictures while
using the program, and see if the dialog boxes have changed. Ideally,
each chapter would be reviewed by one person who is technically
knowledgeable and one person who is not, but that rarely occurs due to
lack of people.
Unfortunately, a lot of "reviewers" appear to read the chapter but
don't follow along using the program, because they don't spot what to
me are glaring differences between the illustrations and the dialog
boxes and thus notice things that need to be updated.
--Jean