A normal drop set involves reducing weight while performing reps to failure. The last set often involves a relatively light weight that might not always maximize fatigue in high threshold motor units. Going back to your starting weight for one more “set” to failure guarantees maximum fatigue in high threshold motor units which is a great stimulus for growth. This method works best on machines, so if you use free weights, make sure you have a spotter to help force out the last few reps. Why just be a monster when you could be the King of Monsters?