Rules Engine- PID controller support

Sorry about the late response, since it was not tagged with rules nobody took a look at this post I suppose. 
Am not sure about the usecase here? how would PID controller help here?

Hey Jonathan, As first step towards introducing data science capabilities within rules engine, we are introducing few Statistical functions(like correlation, covariance, std deviation, variance, median) in this Winter release. However, could you please give us the exact use-case for the PID controller.