A use case for SPDY header compression: http://pix04.revsci.net/F09828/a4/0/0/0.js
request cookies and 5.5KB of response cookies.
That overhead is bad enough to mess with TCP CWND defaults - which means you are
taking multiple round trips on the network just to move half a KB of js.
For HTTP, that's a performance killer! Those cookies are repeated
almost identically on every transaction with that host.
SPDY's dedicated header contexts and the repetitive nature of cookies
means those cookies can be reduced ~98% for all but the first
transaction of the session. Essentially the cookies remain stateless for
app developers, along with the nice properties of that, but the
transport leverages the connection state to move them much more