Ellen Lupton, Type on Screen (p. 49):
Picture modern users consuming a long-form article. Reading their phones on the way to work, they may be deeply immersed during a long commute or distractedly killing time while waiting for coffee. If the content is interesting and easy to read, they might go back to reading the piece while at the office, this time on a desktop or laptop, and again at home on a tablet. Strong web typography recognizes and responds to these varied circumstances.