This way of doing things goes way back to bodybuilders in the 60's and earlier. This traditional of doing thing was to 'bulk up" usign heavy weights and eating a lot of food, then befroe a contest, reversing thing using lighter weights for more reps and cutting food intake drastically. "cardio" or aerobic training was not really part of the equation back then. Later, under the influence of Mentzer and others, bodybuilders started training heavier all the time and doing aerobics- or cardio to help burn fat. Even then though, Mentzer's brother Ray and Casey Viator, along with Frank Zane amoung others would deliberatly train more- therir theory was you want to be a little overtrained before a contest to help break down fat and so that when you stopped the body would supercompensate and "fill out" more.
so its a matter of training for mass off season which usually requires heavier and less frequent workouts and then precontest, focusing on just maintaining muscle mass while losing as much bodyfat as possible.