Why are some saints' biographies considered unsuitable for a dedicated 'Parayan' or 'Saptah'?

The text explains that while certain collections of saints' lives, such as those by Shri Dasganu Maharaj, are valuable, they are not ideal for a 'Parayan' or 'Saptah' dedicated to a single saint. Chapter 0 clarifies that this is because the individual biographies within these larger works are often not comprehensive or detailed. They may only span two or three pages, which is insufficient for the focused, in-depth devotional study that a Parayan requires. For such a purpose, a more extensive and singular biography, like the 'Shri Sai Satcharita,' is considered far more appropriate.