It has been customary to sing
Lokah Samastha Sukhino Bhavanthu
at the end of some devotion sessions. This mantra has been chanted three times after bhajans in Prasanthi Nilayam for years and years. It means, "let all the people in the world be happy" (Lokah has two meanings in Sanskrit, one: people; and the other: world).
In late summer 2008, Bhagawan directed that, hence forward, we should chant
Samastha Lokah Sukhino Bhavanthu
which means “Let all the worlds be happy,” (and thereby all the beings in the worlds). The earlier mantra referred only to this world. The new mantra refers to all the worlds and is broader in outlook.
Please note that no group or Sai Center has to chant this mantra. Whether it is chanted depends on the culture of each Sai Center. But, if you do chant it, chant it as Swami has said.