Because I want an "optimal training". I don't want to do 5 sets if 2 are optimal, train 3x per week is 2x is optimal, train at 100% if 95% enough, etc. Years ago I tried to determinate Optimal Training via theory (it's why I was very interested by HIT and especially Heavy Duty) but now I know that there is only one way to know : TEST IT. It'll take a few years but I may found what's Optimal and eventually be able to build my own theory based on my experiences. I already have my ideas but I need confirmations through practice !