In the days before perfect network connectivity? Both. There are also time delay issues. You want the sensor (radar) the 'computer' and the launch site all close together so they can coordinate the intercept without communication delays, without long radio links that are likely useless during nuclear war.

Sprint was meant for raw speed. It famously accelerated at like 100g. The shortest intercept is one that is launched perpendicular to the incoming warhead. The interceptor goes out vertical as the enemy warhead is coming in more horizontal on its way to the city 400km down the road from the interceptor base.