Most operons in cells belong to higher-level regulatory networks. Most processes in bacteria are too complex to be encoded on a single operon.
Control becomes to complex or inefficient to be practical.
For example, dual regulation of the lactose or galactose or arabinose operons is desirable to that cells don't waste energy producing enzymes for less desirable substrate utilization. All operons that respond to a common environmental stimulus, no matter what regulons or modulons might be involved. A common procedure to recognize proteins belonging to regulatory groups is to radiolabel proteins after a shift to the new conditions. Proteins that become specifically labeled are identified by 2-D gel electrophoresis. Another method is to use a promoter lacZ gene borne on a transposable element.