@Vijayakumar, Vishal Vijay It is optional to enable the private network, but you should consult the chart below to see if your scenario matches any of the listed ones.
Additionally, if you have an Azure AI Search resource protected by a private network, and want to allow Azure OpenAI on your data to access your search service, complete an application form which will be reviewed by Microsoft in 10 days for approval. Refer to the documentation for details.
Thanks
Saurabh