Hierarchy of Configuration File

Configuration files are arranged in hierarchy. Child Web.Config files override configuration settings specified by their parents. This means that you do not need to copy the complete contents of a parent Web.Config file when creating a Web.Config lower in the hierarchy. You can specify only the configuration settings that you need to modify.

Note: If your asp.net application doesn’t consist of Web.Config file than all the settings from machine.config file would be applied.