Imagine that you had a time-delayed cache lookup. If a web server sent different payloads (perhaps a time stamp) on each request, and set the cache control head

Imagine that you had a time-delayed cache lookup. If a web server sent different payloads (perhaps a time stamp) on each request, and set the cache control header to be fairly long, you could determine if something was coming out of a shared cache, or if it was fresh. Hence, we need it to be cached per site (unfortunately)