"We will form a multidisciplinary body of experts to bring a broad perspective to the critical issue of advanced AI."

Endow computer with general intelligence. Apply intelligence to improve upon itself. Lather, rinse, repeat. FOOM! Intelligence explosion.

If prophets of 1900 AD - never mind 1000 AD - had tried to bound the powers of human civilization a billion years later, some of those impossibilities would have been accomplished before the century was out.

Founding, early years and recent progress of SIAI.

Trying to answer directly why superintelligence matters chokes on a dozen different simultaneous replies; what matters is the entire future growing out of that beginning.