Credentials used to log into the portlet determine access for the workloads section including what objects you see, what maps you can use, and which workflows you can manage. Normally you cannot modify or execute the workflows of others. If you have been added to the viewpoint admin role in roles manager, you can perform management functions on other people's workflows.
Credentials added to Monitoring Settings need access to all objects and maps on the system. The TD_Maps user has the access required. The credentials are used for System Monitoring. In System Monitoring, any user of the portlet can see any object and map that the Monitoring Settings credentials have access to. They are not limited as when using workflows.
For more information on database users, see Database Administration.