For browsers capable of talking SPDY (Chrome, Opera, Firefox), this protocol provides:
- Prevention of the browsers to resend information like user-agent, browser properties. In a way, it creates a session state on a normally stateless protocol.
- Avoidance of the HTTP pipelining mechanisms and an ability to prioritize the sent assets to its clients.
- A push mechanism that can pre-fill the browsers cache just like it was doing some page prefetching. If you prefer to lower the outgoing bandwidth of your servers, there are server hints that informs the browsers of the prefetching they could if they wish it.
Guy Podjamy, CTO of Akamai, presents a nice introductory video on SPDY. A must watch.