This option controls whether Squid is allowed to merge multiple
       potentially cachable requests for the same URI before Squid knows
       whether the response is going to be cachable.

       This feature is disabled by default: Enabling collapsed forwarding
       needlessly delays forwarding requests that look cachable (when they are
       collapsed) but then need to be forwarded individually anyway because
       they end up being for uncachable content. However, in some cases, such
       as accelleration of highly cachable content with periodic or groupped
       expiration times, the gains from collapsing [large volumes of
       simultenous refresh requests] outweigh losses from such delays.