[okish]

There is only a certain amount advance the pump can make, and it is in direct correlation with how much travel there is in the timing piston assembly to rotate the cam ring. The timing piston is controlled by the internal pump and by the timing solenoid. Without the timing solenoid, the advance will be solely based off of the speed of the pump. The timing solenoid allows for more advance at lower pump speeds as controlled my the pcm on the pump. A timing box just allows for more timing than what the pcm wants.

Those are my thoughts on it and from experience working on rotary pumps. A VE pump can only control timing by pump speed and my a KSB solenoid to increase case pressures and base timing.