what is advantage of UpdateSourceTrigger in wpf DataBinding?

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WPF

data-binding

hello.
you know that if I bind two TextBox.Text together and set UpdateSourceTrigger="PropertyChanged" , by changing TextProperty of Target TextBox new value is set into another TextBox(Source).
but when i bind my TextBox to a column of Sql server table like following:

<TextBox x:Name="ChargingIDTextBox" Grid.Row="1" Grid.Column="1" Text="{Binding ChargingID, UpdateSourceTrigger=PropertyChanged}"/>

after i change my loaded value into TextBox then result of this changing operation not reflected to the Database until is save my table instance.
so what is benefit of UpdateSourceTrigger in the dataBase fields binding ?
thanks