What are the distinctions made between writing biographies of worldly figures, multiple saints, and one's own Sadguru?

The text outlines clear distinctions. As explained in Chapter 0, writing about worldly Gurus is a worldly service whose importance is limited by time and space and does not yield spiritual fruits. Writing the biographies of many saints is a form of Guru service and does yield spiritual fruits, but it is considered partial or one-sided. In contrast, the most certain path to the ultimate spiritual goal is to write the biography of one's own Sadguru and study it with unwavering devotion.