John
I just spoke to a colleague of mine and Per S. He´s an x-AJ37 driver. Speed brakes is rarely used during normal operations. Main usage is during formation flying to instantly make small adjustments in your position compared to the leader. Throttle is a slow way to decrease speed since there is a time lag in changing thrust level in a jet engine. By deploying the brakes a small light is lit adjacent to the brake, this to make it possible to see if your leader is slowing down in darkness.
Brgds Thomas