It very much depends on the situation you're at. If all is required is an access to one/two shared folders and a printer, configuring AD might not be required. However, if there will be any future expansion of the company, such as additional users, services, e.t.c - managed environment should be considered. AD gives tremendous additional features and "nice" central tools. Such as, central user management, less security overhead over each and every workstation in the organization, policies, software deployments, central changes to workstations, applying security updates ... the list is practically endless.
I would definitely recommend checking into the topic a bit further.