It all depends on how important your natural test production is to you. For most average, recreational bodybuilders, going for 12 wks on, 12 wks off, is a good plan. Competitors tend to run longer cycles and take shorter periods off. They are willing to take bigger risks, in order to meet their goals. How you justify it, is your personal decission. But just because some people are willing to take bigger risks (sometimes dangerous risks) doesn't mean you have to go that route in order to get big.  You can make a keep great gains when coming off. Some of it is going to come down to genetics and part will depend on how much muscle you have. A big factor will be your diet. You can't control genetics, but through diet, you can create an environment that will help you maintain and even grow when off of gear. Of course the gains won't be nearly as fast when you're "off" but you will be able to work on recovering your natural test production, as well as give your cholesterol and orals a chance to get back to normal. 

The best way to know how quickly you recover is through doing blood work. If you go in before you start cycing, you can find out what your natural test levels are. You can check your cholesterol, as well as your kidney and liver function. Then when you want to run your next cycle, go back in and run labs again. If you are back to normal, you are good to go. Some poeple recover faster than others. From what I've seen, younger guys, who haven't run as many cycles tend to recover faster then older guys, or guys who have used a lot of gear. Another factor on recovery will come down to how long you are "on" and what compounds you use. If you are on 20 wks straight, you will probably be shut down harder than if you are on for 6 wks. Test cycles are much easier to recover from than when you use 19-Nors, like deca or tren. Running HCG at 250iu 2x wk, while on cycle will put you in a better position to have a better recovery. I would especially suggest HCG when using a 19 Nor based drug in your cycle. 

Most important to recovery is to do a solid PCT. This will be the best insurance policy you can have to ensure the best recovery, in the shortest time. 

So yes, 12 wks on, 12 off is a good plan.