What is the greatness of charity that is done while conducting pitru karyam? What is the difference between this charity and other charities?

The period when pitru karyam is carried out is considered auspicious. So, charity done at that period is also considered the same.
Notes:
All charities done during a Punya kalam are more valuable
We are doing it as per karma, by associating it with our pitrus. Our Pitrus attained a good status and Since a charity being done during that Punya Kalam is considered as special.