Indexes and tables of contents provide a context, giving a broader snapshot of the field at a given time. And after consulting them, the researcher must make a considered decision to take the next step.
By contrast, in online searches, the researcher tends to follow hyperlink to hyperlink, in a journey that resembles “a plunge down a rabbit hole,” in the words of Robert Berring, a law professor at the University of California at Berkeley who has studied the impact of electronic media. “If you get to an index, a table of contents, you see the environment that surrounds it. In the culture of paper, a lot of these signals are important.”