This is a more advanced exercise that requires great coordination and balance. It's not the type of exercise that should be performed by beginners.
The one-arm alternation engages and challenges your chest muscles in a different way. This is why this exercise is good when you want to change an already existing chest workout routine and add some fresh exercises to avoid hitting a plateau.
It's also worth pointing out that the heavier the dumbbell(s) the more challenging it gets to keep balance. Thus, you may need a spotter to help you out a bit.
Execute this movement with caution and care. Keep the movement at a steady pace and engage your core (stomach) muscles to help you maintain proper balance at all times.