Traditional Sets and Reps Workout vs. Circuit Training

Circuit training brings out the definition of your muscles, that is the shape and definition. It is not intended for bulking up/increasing copious amounts of muscle mass. Circuit training has higher reps with lower weights involved in the workout. This changes the chemistry of the muscles being worked.  This results in increased lactic acid build up which has a positive effect on both metabolic rate and hormone release.
The major focus of traditional strength training is on isolation of an individual muscle to maximize overload and increase of muscle mass.