XML-RPC was added in WordPress 3.5 and allows for remote connections, and unless you are using your mobile device to post to WordPress it does more bad than good. In fact, it can open your site up to a bunch of security risks. There are a few plugins that utilize this such as JetPack, but we don’t recommend using JetPack for performance reasons.
In the perfmatters plugin you can easily disable this by enabling the “Disable XML-RPC” option.
You can verify that XML-RPC is disabled by using this free XML-RPC validation tool. If you get an error such as the one below then you are good to go.
This also removes the XML-RPC HTTP response header associated with it.