Original: Another advantage of supersymmetry is that supersymmetric quantum field theory can sometimes be solved. Supersymmetry is also a feature of most versions of string theory, though it can exist in nature even if string theory is incorrect.
Simplified: Supersymmetry is a of theory (commonly found in some forms of string theory) that says that when the universe was made, there was also the same number of theoretical "superparticles" created.