I wouldnt recommend using less than 50 percent of load. As we go below 40% of 1RM, it comes more of a cardio activity. This is upwards of 30 reps. We get tired because the set is taking so long, so we can't actually train with the required intensity to go close enough to failure to stimulate an hypertrophic adaption. Whether we train with 6 reps per set or 30, we need to be within 1-3 reps from failure. At the end of the day, using loads below 50% of 1RM are an inefficient and probably ineffective use of our time.