A feed is the one part of a site that other programs read directly. That makes it unusually unforgiving: a single unescaped ampersand and a reader stops mid-file. This check reads the feed links from the page, fetches them and reads back what a reader actually needs.
From this server: one request for the page and up to three for feeds, each capped at 1 MB. No cookies are sent, no scripts are executed, nothing is stored beyond the rate counter.
Limits worth knowing: only feeds linked in the served HTML are followed. When none are linked, /feed/ and /rss.xml are tried — a site using another path will be reported as having no feed, which is exactly what a reader would conclude.