Yatinam Mahalaya is observed during Pitru Paksha period on the 12th or the Dwadasi day in the Bhadrapada month and is dedicated to Sanyasis or Yathi. In 2017, Yatheenam Mahalaya is on September 17. On this day, Pitru Paksha Shradh is not performed for other forefathers. (Please note this custom is more famous in
South India especially with some Hindu communities in Karnataka and Andhra Pradesh).
The reason for performing the Shradh for Sanyasis and saints is that they have preserved and passed on the knowledge of Sanatana Dharma and had done great service to the society.