A regulated pathway behaves differently from an unregulated one. In a regulated pathway, the end product Z inhibits an early enzyme, so as Z accumulates, flux through the pathway falls. The system settles at a steady state where the rate of Z production matches the rate at which Z is used by the cell. If demand for Z rises, Z concentration falls, inhibition is relieved, and flux increases to meet the demand. If demand falls, Z accumulates, inhibition strengthens, and flux decreases. The pathway tracks demand.
In an unregulated pathway, the feedback loop is absent. Flux is set by the upstream supply of substrate and by the activities of the remaining enzymes, none of which respond to Z. If demand for Z falls, Z simply accumulates because nothing slows its production. If demand rises, the pathway cannot increase its output beyond what the fixed enzyme activities allow. The pathway no longer tracks demand; it runs at a rate determined by supply, not need.
This simulation lets you compare the two cases directly. You control the demand for the end product and, in the regulated case, the strength of the feedback inhibition. In the unregulated case, you can see that changing demand has no effect on flux: the pathway keeps producing Z at the same rate whether the cell needs it or not. The gap between production and demand is the measure of how badly the pathway is uncoupled.