I think it depends on how you train mainly as to how often taking a week off is necessary. It also depends on your specific ability to recover. Not everyone is the same in that regard. Nutrition plays a factor too, as does rest/sleep...and of course your age.
It's different for everyone. I know for me if I am going very heavy in a "blasting" phase, that I can only handle that for about 6 weeks until my body needs a week off. Then I ramp back up by going 2 weeks at 60-75% intensity before going all out, 110%, balls to the wall, heavy ass lifting again.