its not really they way they are used.
They tend to be an extension of the Instructor brief with also more in depth theory behind things along with additional diagrams.
Some people like to turn up with all the info in there heads already so they don't get a head explosion during the brief.
Others like to revisit the lesson afterwards and then link what they experienced with what's in the book.
And others are quite happy doing neither.
Its just a fact that people learn in different ways, if any of the options works for an individual its perfectly normal and nothing unusual for different students to progress using any of them.
The problem only occurs when instructors try and force their method of learning onto students and are inflexible to their students needs.