Control State vs View State

When you are deciding what should go into control state and what should go into view state, remember that it should be a separation of behavioral state from content or UI state. Things like properties and collections of data should generally stay in view state and not migrate to control state. State that triggers a server-side event is the most typical type to store in control state.
Declarative Data Sources and View State
In simple case, if we have not disabled view state on the GridView, you may think that we are again just wasting view state on storing data that is never used. Fortunately, the ASP.NET 2.0 engine makes the extra effort to do the right thing here, and it will not bother going back to the database when view state is enabled on a control.

Similarly, if you disable view state on the GridView, the data binding to the data source will occur on each request including POST back requests.
This functionality is built into the DataBoundControl base class from which the AdRotator, BulletedList, CheckBoxList, DropDownList, ListBox, RadioButtonList, GridView, DetailsView, and FormView controls inherit. All of these controls exhibit this intelligent use of view state when bound to declarative data sources.

Reference : http://msdn.microsoft.com/msdnmag/issues/04/10/ViewState/