What are the two primary forms of service a Sadguru receives from devotees in relation to books?

According to the preface in Chapter 0, a Sadguru takes two distinct types of service from devotees through books. The first is when the Sadguru creates great works themselves, with examples given such as the Shri Dnyaneshwari or Shri Dasbodh. The second form of service is when the Sadguru has their biographies written by their devotees. In this case, the Sadguru accepts service through the study and devotional readings, or Parayans, performed by both the writer and the wider congregation of devotees who engage with the biography.