Swimmers Stretching Before Your Swimming Workout

Is it a good idea for a swimmer to stretch before getting in the swimming pool? How many times have you seen swimmers stretching before they get in the pool? I can't count that high! We have been told that flexibility is important for increased performance ability and to decrease the occurrence of injury. Is it? It may be more important to stretch at the right time - or it might be a waste of time. Should all this stretching be done before you swim?