Too many people waste their time by, saving their strength for the duration of their workout. I try to beat the hell out of my muscles starting with the first set. Only a small percentage of people do negatives at all. They like to drop the weight. They feel that if they do negatives, they will be weaker on the following sets.
Negatives are a fully functional part of any workout.
They must be accomplished. If you do not lower the weight during every set, you will not receive the gains that you anticipated. Remember a workout is just a workout. A workout is not a means of justifying strength. A workout is a tool to gain strength.