There are times when huting with the wind off your shoulder is far superior to hunting with the wind at your back (which is the tried and true method of duck hunting). Obivously when you have the wind at your back you are attempting to get the ducks to land directly towards you as they approach your duck decoys. This very reason is a key tenet in why you might want to hunt with the wind at your shoulder (i.e. a crosswind). If they ducks are coming directly at your duck blind, they by default me be looking in your direction. This may be fine if they are young birds, new birds, or you are extremely well hidden. If you are in a spot that doesn't lend much cover or the birds are wary, this can tend to flare birds as they prepare to finish. This is the main reason I hunt with the wind at my shoulder. The birds will be finishing across the blind, but are not looking directly at me as they prepare to land. If you set your decoys close enough they will still finish in close range and allow for high quality shots.
Below is a Video showing how to hunt a crosswind and the key reasons for doing so.