You might be happily surprised to learn that your teachers don't always expect you to read in depth. Students might not know when to skim and when to read in depth. Developing the judgment of when to skim, or at least when to ask if they should skim, can save a significant amount of time and energy which can then be channeled into more high value work. Knowing when to skim might be particularly helpful for students with slower processing speed or weaker attention.