If there were no unmeasured disturbances, feedback control would not be necessary. Process engineers and operators could home in on the best PID output and just leave it at this value. In fact many process engineers are much more comfortable with setting a stream flow per a process flow diagram...
What configuration changes to control strategies can readily take advantage of improvements in measurements and final control elements? Control strategies can inherently improve production rate by maximizing feed and efficiency by enforcing material and energy balances.
When we saw an increase in production rate needed during opportunity assessments at Monsanto and Solutia, we would salivate. Impressive results could be obtained in a matter of a few days by a simple change in setpoint, tuning, and/or configuration.