Many people have a "dominant" side in the weight room. One arm is stronger. One leg is stronger—or even longer—than the other.
This creates an interesting situation in your muscle systems. If one side is stronger, it will move more of the weight and become even stronger than before! So, how do you fix that imbalance? You use dumbbells, where each arm holds the same weight and must move it alone. And you do single-leg exercises like deadlifts.
These one-sided exercises help your actual balance while also giving more balance to your strength systems and aesthetic appeal.