The "Office Client Policy Service" allows the administrators to define policies for Office 365 ProPlus users and assign policies to them via Azure Active Directory security group. Once the policies are defined, they are automatically enforced as users sign in via Office.com/setup and use their 365 ProPlus applications such as Word, Excel, PowerPoint, Access, and Outlook. Currently, the preview is limited. It simply maintains, "a subset of user-defined policies defined in ADMX templates". However, Microsoft clarified in their announcement, all the machine-based policies are not included.
It is stated that the Office Client Policy Service only if the Office Setup 365 ProPlus accounts of their end-users created in Azure Active Directory, which is Microsoft's identity and access management service. Office setup is still able to download and install Office setup 365 ProPlus.