what is an advantage of a domain?

On the contrary, that question can only be understood by an applicant who knows that “Domain” here refers to applying the ISO 27001 standard. It has nothing to do with your website.

Central management and organization of a group of devices, users, and resources.

This question was obviously asked by someone who knows nothing about security. What is an advantage of a domain? What type of domain were they asking about? Physical? The name in a DNS? A logically separated environment? You are lucky you were not hired. The VP in charge is unethical and intolerable. Most people there don't like or trust him but he is protected by the COO.