Assuming Person A and Person B exercises their muscle groups twice per week for maximum hypertrophy. Considering that the only thing that seperates the two men is how they approach their workout, which one of them will utilize the aformentioned hypertrophic frequency the best? For example Person A: Does 9 sets of flat bench chest exercises, followed by 9 sets of decline bench chest exercises three days after. Person B: Does 9 sets of flat bench chest exercises and repeats the same three days after. NOTE: Person A shifts his focus to lower chest, how much of a role does hypertrophic frequency play here (if any).
Every body is different. So there are no set rules anyone could follow for sure fire results. With body building it takes years, many tries, knowing your own body more and more and experience to figure it all out. So to give definite advice is not 100% possible. That said, my 35 year experience in the sport is, that muscles get bored easily. To switch exercises has always been good advice for me. I would prefer, if I workout each muscle group twice weekly to do different exercises each time. Since every exercise hits slightly different muscle fibers, at an different angle as well as stretches it differently on the negative movement, this promises maximum efficiency for my workouts. You might tire and overwork your muscles too much by doing the same exercises twice a week. Muscles grow when they rest after having been hit in the gym. Three days later seems too short of a break in between for doing the same routine again. All of this is really personal experience and the only real concrete advice I can give you is to experiment and be inventive in your workouts.