The Gironda lateral raise is a variation of the traditional lateral raise. By tilting forward at the hips, and positioning each dumbbell as though you are pouring water from a cup, you put your shoulder in a position that best targets those lateral deltoids.
Though the shoulder-press is a good exercise for building overall mass in the shoulders, the rotational position of your shoulders during this movement, means that there is very little targeting of the lateral deltoids.
The reason boxers have such big rounded shoulders is because while throwing a punch, your arms and shoulders are in the optimal position for targeting those lateral deltoids. This position is simulated very well by the Gironda lateral raise.