I think the Referer header kinda-sorta serves as mitigation for 3rd parties just (maliciously) hot-linking to, say, images on your domain, effectively forcing y

I think the Referer header kinda-sorta serves as mitigation for 3rd parties just (maliciously) hot-linking to, say, images on your domain, effectively forcing you to bear the cost of upload bandwidth for those images. (And similar, it's just that images sprang to mind.)