It depends on whether you mean if light travelled at 700 miles an hour, or sound at 286,000 miles a second. If the former, and the same slow speed applied to all electro-magnetic waves, then surfing the web would be a pretty dismal experience. If the latter, it would make it much easier for large choral groups (eg cup final crowds) to synchronise their singing. Seriously, this could only be the case if one imagined an entirely different universe with different physical laws, which would have led to the evolution of a different human species (if any), which would be asking on ITS Answerbank "What effect would it have if the speeds of light and sound were different?".