Users typically interact only with completed dashboards -- data and UI -- provided by IT or another development team.
With the "Server Objects" feature turned on (default) end users may create addtional charts or other sheet objects (such as listboxes) in the dashboard using only the data provided in the document. By default, these user created objects are visible only to the user that created them. The user may then explicitly share the object with one or more other userids.
Creating user objects is usually only done by power users. Typically, the dashboard should provide the common ("Document") objects necessary to satisfy the analysis requirements of most users in the organization.
A common scenario is that IT or other "data experts" code the script to build the data model. And then they task business power users or analysts with building the Document UI (screen objects) for all users.