# Is it important to have a good behaviour inside internal loops of a cascaded PID controller?

A cascaded PID controller is depicted in following image (courtesy of controlglobal.com):

The primary PID tracks the setpoint $SP_1$ and delivers a setpoint $SP_2$ to the secondary PID.

I wondered if it could be a problem if the secondary PID does not have a nice behaviour w.r.t. tracking its setpoint, while the total result of the cascaded PID controller is OK. This would mean that the overall tracking of $SP_1$ is OK, which is the goal of the total controller, while some internal controllers are not tuned too well.