I read Ben Johnson did 3 weeks on, 3 off. Supposedly allows body to recover from increased Ldl levels and other side effects...common in the Canadian track team. . the theory is that the off cycle time solidifying gains, allowing your body to reset its plateau or resting point, and adding more during the following two weeks. Again solidifying the gains before adding more mass.
Sure takes longer, but to my mind just makes sense...I might add I haven't done it yet, but interesting theory.