Explanatory conviction of the implementation of the domain structure, how?

Question

Domain name market

Good afternoon. There is a small firm. It has ~20 workstations and 1 nas server. All access rights are given as local users. Proposed to introduce a domain structure. But the customer does not see the need for this.
Please let me know what are the pros and cons. I see the point of introducing a domain structure, as the company grows and people will be added, as well as workstations. Convenient administration
Thank you for your attention.

Answer 1

plus one. the speed of patching when finding holes.