Which two main types of service does a Sadguru accept from devotees through the medium of books?

According to the preface, a Sadguru accepts two primary forms of service from devotees through books. As outlined in Chapter 0, the first type is when the Sadguru creates a great literary work themselves, with examples being Shri Dnyaneshwari or Shri Dasbodh. The second type of service is when the Sadguru has their biographies written by their devotees. In this case, the Sadguru accepts service from both the writer and the congregation of devotees who engage in the study and Parayans (devotional readings) of that biography.