According to the text, what distinguishes a truly effective biographical work for community building from less useful ones?

The preface in Chapter 0 draws a clear distinction between effective and less useful biographical works for community building. An effective work, suitable for devotional readings like Parayans and Saptahs, must be detailed, poetic, and comprehensive. The text contrasts such works with biographies that are not comprehensive, sometimes spanning only two or three pages, which are deemed not useful for this specific purpose. The Shri Sai Satcharita and the Guru Charitra are held up as prime examples of effective works because their detailed and graceful nature allows for daily study and group readings, which in turn fosters a strong and engaged community of devotees.