Unilateral or one-handed exercises force you to recruit more core muscles to stabilize the spine and transfer load in ways neglected by bilateral lifts.
The dumbbell hang snatch is knows for building traps and boosting athletic power, but it's also a core strengthening exercise. It provides a missing component in most lifter's ab training – high-velocity movement. 
Using a total body movement like this requires your core to contract and transfer force. Your abs contract to stabilize the unbalanced weight overhead. This results in abs as strong as they are visually appealing.
Start with a dumbbell between your legs in the hang position (not resting on the ground). Fire the dumbbell upwards by driving through your heels and fully extending the hips. Drive the elbow high and catch the dumbbell overhead with the knees slightly bent.