I agree chubot++, the knowledge you gain (ROI) is more important rather spending time reading possibly non relevant "filler".

At university, certain professors (aka one really naughty chemistry professor) expected complete mastery of the subject and would have several questions in the examination that were not even covered by the assigned reading. (He expected us to read the entire textbook anyway)

I also prefer technical manuals in PDFs and just CTRL+ F through them as needed.