When we’re working on speed, power or maximal strength (rather than aerobic or anaerobic conditioning or muscular endurance) you need to take sufficient rest to ensure that the body can continue to operate at the level necessary to best train those qualities. To train those qualities you need to be relatively fresh. You can not be overly fatigued and expect to train speed, power or maximal strength well. To train these qualities, one needs to be able to recruit muscle fibers maximally and efficiently. When someone is overly fatigued this is not possible. So while there’s certainly a time and place for fast-paced, minimal-rest workouts or portions of workouts, that would be inappropriate if the goal of that workout or portion of the workout was to train maximal strength, power or speed.