Two black holes takes the theory into a dynamical regime, where you can make predictions and then, if experiments verify the predictions, you know how far the theory is correct. It's a mutually beneficial relationship. To verify the predictions, you need detectors. LIGO, Virgo and GEO600, likewise, need predictions. Many believe that colliding black holes is the best shot at detecting gravity waves.
Theory says it's one of the strongest signals on the gravity-wave dial.
To know if a crackle of static is the dance of two black holes or cosmic noise, the detectors need the answers numerical relativists are working to provide. He might have said the same about the event horizon of a black hole. In solving Einstein's equations, Schwarzschild started with the idea of an infinitely condensed mass and showed that space-time curves around it and closes on itself. The region inside the horizon is cut off from events outside. This principle, called cosmic censorship, underlies black-hole excision.