From what I understand, India does not allow dual-citizenship. Because of that, they have PIO (now OCI cards) for people who are originally from India but were granted citizenship elsewhere.
The benefits of the OCI card, according to this website:
Indian Visa | India Visa Application | Faqs | Oci | General Oci Questions | What Are The Benefits Of An Oci
"The following benefits will be allowed to an OCI card holder:
- Multiple entry, multi-purpose lifelong visa to visit India
- Exemption from reporting to Police authorities for any length of stay in India
- Parity with NRIs in financial, economic and educational fields except in the acquisition of agricultural or plantation properties."
It seems as though they will no longer receive the benefit of visiting India as often/for as long as they please without obtaining a visa, but I'm not sure. Hopefully someone with better knowledge can better explain.
According to this article
India to cancel OCI cards of Sherin Mathews’ foster parents, relatives in U.S.
They were looking to make the recommendation of blacklisting them, which I believe means they would not be able to gain entry for even just a short visit.