if germany blew up the radar sites uk would not have been able to scramble their fighters to the exact spot needed to stop the german squadrons, thus germany would have been able to better bomb the airfields and airplane factories.
the only reason they started bombing cities willy-nilly, was one of their bombers accidently bombed a city, and uk responded by bombing a german city and that escalated the city bombing war on both sides. if germany stuck with its plan, even with uk radar functioning, they would have destroyed the airfileds and would have thus dominated the sky. :evil: