Running an immutable setup in production
The file containing the credentials for accessing the database, and other site configurations (e.g. the proxy settings, the trusted domains), is inside the server document root (for example, sites/default/settings.php). The answer to Is there any reason for which the content of the server document root would need to be changed when deploying to production? is then yes.

Add to this the fact that the directory for the public files (e.g. the uploaded images attached to nodes) is by default sites/default/files, you have a reason more to preserve one or more directories under the server document root directory in the production environment.