what is the purpose of link rel="pingback"?

Question

What is the purpose of <link rel="pingback" href="<?php bloginfo( 'pingback_url' ); ?>"> ? It appears in the default wordpress 2014 theme but pingbacks work without it .

Answer 1

Pingback URLs may be exposed via HTTP headers, so removing them from the HTML while the HTTP headers are intact is fine.

Having them at both places would help clients that only support one way of discovering pingback URLs, but most implement both. Using headers is even better because clients can do HTTP HEAD requests to discover them and do not have to fetch and parse the whole HTML.