The process of expressing genes is an energy-requiring process since it requires the breaking and synthesis of proteins.
When genes are regulated energy is saved as only the gene required to perform a certain job is turned on and after the function is completed it is turned off. Therefore, continuous protein synthesis is not required to express the genes at all times.
If the genes were not regulated i.e., turned off and turned on at required times then it would take a never-ending spree of gene expression which in turn would require a lot of time in transcription and translation.
