A superset is a training technique in which you perform any two exercises consecutively without resting in between. Supersets can be more effective when the two exercises performed either involve antagonistic muscle groups or unrelated muscle groups. For example, performing shoulder presses and squats one after another (Unrelated muscle groups) or getting in a set of bench press and dumbbell rows (antagonistic). This effectively doubles the amount of work you are doing, while keeping the recovery periods the same as they are when you complete individual exercises.
You’re short on time. Period. Maybe you want to add in more exercises to your workout but cannot increase the workout duration. Or you simply do not have the time to indulge in rest between sets.
Classic instances of muscle pairings for supersets include:
Going by this very simplistic guideline, you may choose to do a bench press followed by a seated row. While you trained the latissimus dorsi for the row, the pectoral muscles involved in the bench press got their needed rest. Another good example is performing a squat followed by shoulder press. Squats and shoulder press target very different muscles in your body and as such performing them consecutively is okay.
Although, supersets are a good idea when you’re crunched for time these should not be be a consistent practice as it reduces your ability to lift the maximum weights due to insufficient rest periods. Supersets are in no way superior to the traditional sets when the volume (work done in a training session) is matched. One thing to remember is supersets effectively reduce or even eliminate rest periods. It is not the right choice if your goals are to increase muscular strength or power. Complete recovery between sets is essential to training for strength and power.