Please note that by default the map's full extent is defined by the full extent of the map published on ArcGIS Server. However, on the client side you can override the map's full extent through SetFullExtent method, and the new full extent property will persist for the whole life cycle of your local map cache. Also note that when you synchronize your data with server, the client side full extent property will not be synchronized.

For differences between map extent, view extent, and rotated extent, refer to the GetViewExtent method.

Reference