@simon I think it is useful to have resource variants that are also addressable by URL, like /calendar/x/1.ics vs /calendar/x/1.html or /calendar/x/1.json. But that you can have /calendar/x/1 and have that resource serving the proper thing via Accept, is an HTTP superpower to me.
@helge I get the theory, but in twenty years of mucking around on the Web I've never actually seen real concrete benefit from APIs that do that - I've just found it frustrating