Most training programs are based on a standard set routine—performing a specified number of sets of an exercise, then moving on to the next exercise. However, this may not be the most effective and efficient method for making strength gains.
A recent study in the Journal of Strength and Conditioning Research found that performing paired sets—commonly called supersets—actually produces greater strength gains than traditional sets. In the study, the paired set involved two exercises that alternately activated an agonist muscle (the primary one involved in an exercise) and the antagonist muscle (the one that works opposite the agonist when returning to the start position). In the Bicep Curl, for example, the agonist and antagonist muscles are the biceps and triceps, respectively.
Study researchers had subjects perform a Barbell Row variation and the Bench Press in superset fashion, with a two-minute rest between them.  They found that supersetting opposing muscle groups promotes faster recovery, allowing an athlete to perform subsequent sets with more reps or heavier weight for an elevated challenge. Also,  when you superset two exercises that engage opposing muscles, you are also activating other muscle groups in your body more than with traditional sets that work the same muscle groups.
For more information about adding supersets to your workout, check out these STACK-exclusive exercise videos with Oklahoma Baseball and Real Salt Lake:
Oklahoma Baseball performs the Alternating DB Bench and supersets them with Pull-Ups.
Real Salt Lake develops explosive upper-body strength by performing the Push Press and Chin-Up in superset fashion.
Source:  Robbins, D. W. (2010). The Effect of an Upper-Body Agonist-Antagonist Resistance Training Protocol on Volume and Efficiency. Journal of Strength and Conditioning Research , 24 (10), 2632-2640.