Why are some spiritual works considered unsuitable for a detailed Parayan of a single saint, and what is the benefit of performing one with a suitable text?

The text in Chapter 0 explains that some works are not suitable for a Parayan or Saptah focused on a single saint's life because they are not comprehensive or detailed enough. For instance, some biographies may only take up two or three pages, which is insufficient for this purpose. The benefit of performing a Parayan with a detailed biography, like the Shri Sai Satcharita, is twofold. For the writer, it is a form of Guru service. For other devotees who study and perform the Parayan, the writer gains merit for public service, and the devotees themselves are helped to achieve the purpose of their lives.