This setting overrides some important application level security settings that are usually used for debugging and development and prepares the server for the real-life production use:

        <configuration>

            <system.web>

                <deployment retail="true"/>

            </system.web>

        </configuration>

To be precise, this will enforce the 'debug' flag to false in every web.config on the machine.
Also it will disable page output tracing and it will force the custom error pages
to be shown to remote users instead of the real error messages.

note:
This value can only be set at the machine level, not at the application level.