Repetition maximum sets and workouts create the optimal stimulus for strength and tone.
If you are lifting weights I feel you should get the most benefit from the time spent. And that is obtained by doing RM sets. If you lift lighter you are not forcing the muscle to recruit (use or train) all the muscle fibers, particularly the type IIb muscle fibers. And an untrained muscle fiber looks flaccid and untrained - almost like fat, loose, giggly, ... you get the picture.
Without RM sets you don't train all the muscle fibers and therefore don't get the most from your lifting. And intensity is the primary stimulus for adaptation, with lifting RM sets dictates the intensity. Rather than doing a set of 8 repetitions with a light weight which you could possibly lift for ten twenty even one hundred reps, an 8 RM set dictates that the eighth repetition is the last that can be performed, no more - no less. The RM designation sets the intensity of the workout.
Supersets act as active recovery days where the muscles are trained albeit at a lower intensity to enhance repair, remove waste products and enhance delivery on essential nutrients for growth and repair. And supersets are more time efficient than straight sets. Since this workout is not at a maximal intensity, rather at approximately 80 - 85 percent of max the lack of rest between sets is not an issue and provides an added motivational tool since it switches the workout around a little - more variety, less burn-out.
The primary changes you and the others are training for are improved muscle strength and tone. In time, your muscles will be stronger - to aid in daily activities and allow less stress from your outside tasks. In addition, they will be more toned, aiding in appearance and well-being.
Two other forms of resistance training are for power and size (hypertrophy) training. Both of those types of training are different from what most everyone is doing and the adaptations are different from those you are getting.