Hi:
If you had the SAS Add-in for Microsoft Office and NEVER used a stored process, the Metadata server would use the Workspace server to authenticate/authorize user access to data and would use the Workspace server to "serve" data for Add-in tasks.
However, if you DO use stored processes, then when you register the stored process in the metadata, you have the choice to specify either the Workspace server or the Stored Process server as the server of choice for stored process execution.
There -are- differences in the type of results that can be generated and returned to client applications using each server type. There are also authentication/authorization differences with each server. These differences are outlined in the stored process documentation and in the Platform administration documentation.
You should ask your SAS administrator for more details about your site's configuration and their reasoning behind configuration decisions.
cynthia