Dumbell flies are a great over all mass and detail exercise for your chest.  Its awesome for shaping and for building.  This movement pulls the arms across the body.  This is the basic function of the chest muscles in the first place.  By giving your pecs such a stretch at the bottom of the movement it allows them to fill with blood and grow.  You just have to ne careful of your shoulders when you do this movement. If you have a prior shoulder injury then you should consult a doctor before you do this exercise.  Its also a good ab and oblique exercises