This is a classic dumbbell exercise for the chest. It's very effective and will pack on slabs of muscle onto your chest in no time. The key to this exercise is executing the movement accurately. Once you get into heavier weights (dumbbells) you may even need a spotter to assist you.
This exercise is great for either a bulking-up phase or a definition cycle. The only difference being that if you're trying to put some mass on your chest, you will go with heavy dumbbells. Conversely, if you are on a muscle definition or fat burning cycle, you will select lighter dumbbells and go for more repetitions.
Another thing worth pointing out is that you will need to focus on getting yourself balanced right. The heavier the dumbbells, the more challenging this exercise will become in terms of executing the movement in perfect balance. This is one of the reasons this exercise is so effective - it employs/involves many muscles in the execution of the overall movement.