Good question. I think I remember reading that for weight workouts, you should try and stick to a rotation for weeks. For example, do S&H for 3-4 weeks for strength/size, then switch to endurance workouts like Powerhour for a month or so.
I see slightly better results when I focus on one type of workout for awhile vs constantly switching. I used to think switching it up was best since you're suppossed to mix up your cardio. But I was wrong.
I could be completely wrong though!!