The Dashboard allows you to cycle between 3 states:
 Full: the Dashboard Header is above the grid and one of the tabs is open
Collapsed: the Dashboard Header is above the grid but none of the tabs are open 
 Floating: the Dashboard appears as a small control which you can drag where you want. 
But you can, additionally, hide the Dashboard altogether by setting the IsHidden property in Dashboard Predefined Config (as done in this example).
The Dasbhoard can be made visible again by clicking Dashboard / Show in the Column Header Menu or via the Dashboard Tool Panel 
Note: you can hide the Dashboard completely by setting the 'Dashboard' to be Hidden in Entitlements and then it can never be made visible again.