WIthout this directive apache will try other default/global DirectoryIndex files resulting in useless file access/error messages in logs
```
[Sun Mar 07 14:04:25.383960 2021] [authz_core:error] [pid 946:tid 139985284290304] [client 10.0.0.1:42616] AH01630: client denied by server configuration: /var/www/links.example.org/index.html
[Sun Mar 07 14:04:25.384293 2021] [authz_core:error] [pid 946:tid 139985284290304] [client 10.0.0.1:42616] AH01630: client denied by server configuration: /var/www/links.example.org/index.cgi
[Sun Mar 07 14:04:25.384465 2021] [authz_core:error] [pid 946:tid 139985284290304] [client 10.0.0.1:42616] AH01630: client denied by server configuration: /var/www/links.example.org/index.pl
```