ConfigSource property in Web.Config file

configSource
You can use the configSource property of a ConfigurationSection to specify a separate file where the configuration of that section is stored.

Ex: All Connection strings are stored in a separate file "ConnectionStrings.config"

Content of ConnectionStrings.config

  

         connectionString="Data Source=(local);Initial Catalog=Sample;Integrated Security=True;MultipleActiveResultSets=True"
       providerName="System.Data.SqlClient" />

         connectionString="metadata=res://*/MatsModel.csdl|res://*/SampleModel.ssdl|res://*/SampleModel.msl;provider=System.Data.SqlClient;provider connection string="Data Source=(local);Initial Catalog=Sample;Integrated Security=True;MultipleActiveResultSets=True;Application Name=EntityFramework""
       providerName="System.Data.EntityClient" />

Benefits

1. Using include files can result in a more logical and modular structure for configuration files.
   
   
2. File-access security and permissions can be used to restrict access to sections of configuration settings.
   
   
3. Settings in an include file that are not used during application initialization can be modified and reloaded without requiring an application restart.