I think the biggest reason some people (such as myself at times) go only eight weeks is because your testosterone recovers faster the shorter the cycle duration is ran. For example, your natural test will recover much faster on a six week cycle than a twelve week cycle. However, unless alot of gear is stacked heavy for a long period of time, say more than five or six weeks, most people can recover with average to minumal difficulty. It's when cycles start running 12-16 weeks or so that recovery becomes a problem for most. Anyhoo, the theory that the shorter the cylce, the easier the recovery, is still a substancial one and has proved it's self according to my experience. (For whatever my exp. is worth)