Often what I’m looking for in a document is a particular image or diagram I remember seeing, embedded somewhere in e.g. a long journal paper or textbook. I know enough to know what section of the paper or book it’s in, but I haven’t a clue what exactly it was labelled, let alone what the specific context was. But I can picture the diagram, so I’ll know it when I see it again, whizzing by. I just don’t need to whiz by the entire document, because I can be sure I saw it “in the middle” or “near the end.”