Use the SaveControlState method to save state information required for the operation of a specific control. This control-state data is stored separately from the control's view-state data.
Custom controls using control state must call the RegisterRequiresControlState method on the Page before saving control state.
Notes to Inheritors
When control state is saved, a string object is returned to the client as a variable that is stored in an HTML HIDDEN element. Override this method to extract the state information to use in your control.
Control state is intended for small amounts of critical data, such as a page index or a keyword. Using control state for large amounts of data can adversely affect page performance. For more information, see ASP.NET State Management Overview.