How previewing sections of a book rather than simply reading them help you to understand the material?

Previewing or reading the entire material has different outcomes. For example, if you are just scanning for simple ideas, be aware that this material will be not retained. This also varies from person to person must people do not like to read long chapters with tedious topics. By the other hand, as an ESL writer I need to read the whole material to be able to understand and also generate questions for my instructor for a better comprehension and avoid to be stuck in the literature. In addition, previewing can be very convenience when the material is extensive and intensive. We are going to read it at least three times before the concept can be retained in our brain as fresh and new information in our database.