This makes the data in your Grid View is available in the Page Load event...including data entered by the user.
I like to be in more control of my database connections. You could do this in your Page Load event if you want to.
Data Source property to the object you are using..call the Grid View.
Data Bind method to bind the Grid View to the data source.
This thing I have done in data acces layer class where I make a method of an update.
I want to use this method so I can do an update in grid view directly. Grid Views can bind to Data Tables, Data Views, Arrays of Objects ..more.