Did you know that originally Quentin Tarantino's Kill Bill was supposed to be one four-hour movie? Later, he decided to make it a two-part deal, allowing him to give each part a very different feel and tone. It also happened to George RR Martin with the Storm of Swords book: it grew so big that he eventually had to split it in two volumes, so we don't have to read a 1,300-page book.
Varnish Cache will try to write as much of the response headers and body to the client as fast as it can accept it. We do this using writev() to let the kernel handle this for us, instead of tying up a worker thread for it.
When Waoo, a content and fiber broadband provider in Denmark, needed to scale for their massive video content delivery needs and to create their own CDNs that could serve traffic both inside and outside their own network, they looked at Varnish Plus to help deliver fast and reliably.