How does the allow_url_include directive impact the ability to include PHP scripts from external servers?

The `allow_url_include` directive impacts the ability to include PHP scripts from external servers by controlling whether the `include`, `require`, `include_once`, and `require_once` functions can load files from remote locations using a URL. Setting `allow_url_include` to `Off` in the php.ini file can prevent potential security risks associated with including remote files.

ini_set('allow_url_include', 0);