If your goal is hypertrophy (body building) you need to choose a weight that is between 70% and 80% of your 1RM. If you always lift a weight that is too light you will never recruit enough muscle fibers to maximize and stimulate hypertrophy. Likewise, if you always lift the same heavy weight every week your muscles will quickly adapt and hypertrophy will stop.
Hypertrophy responds best to changes in “relative” weight and this means you need to constantly change your workout program just like we do in STS. This is one of the reasons why we vary the intensity and exercises almost every week in STS to keep your muscles constantly confused and challenged. We also add little tricks like “Back-off Sets” , “Wave Loading” and “Drop Sets” to further keep your muscles challenged and avoiding plateaus.