I have been diving for about 11 years when I am quarry/lake diving I dont pay it no mind ,I even do it floating on the surface and talking to the other divers about our dive ,but if we were on a ocean dive then I dont do it and if I saw a diver on a ocen dive with there mask on there head I would check them,,,I feel in a quarry its more controlled then the Ocean ,,I was taught the same as others not to do it ,,only when there is a problem ...............!!!!!????