On a typical secure TCP connection, it typically takes two or three round-trips before the browser can actually start receiving data. Using QUIC, a browser can immediately start talking to a server it has talked to before. QUIC also introduces a couple of new features like congestion control and automatic re-transmission, making it more reliable that pure UDP.
via Google Wants To Speed Up The Web With Its QUIC Protocol | TechCrunch.
Users who connect to YouTube over QUIC report about 30 percent fewer rebuffers when watching videos and because of QUIC’s improved congestion control and loss recover over UDP, users on some of the slowest connection also see improved page load times with QUIC.
Google says it plans to propose HTTP2-over-QUIC to the IETF as a new Internet standard in the future.