I think people are taking about different things. You could surface and simply swim 20 or 30 yards to the boat with the reg in your mouth and it’s not a big deal. But swimming any distance breathing down a tank is silly. You could roll on to your back and breathe looking up at the sky but you’re going to have to turn to look where you’re going and every time you do you could get a mouthful of water in any kind of sea. A shore dive could have a number of interesting spots with a distance between them and the most efficient way to move between them is saving your air on the surface and swimming face down with a snorkel. I could reverse my car down the road but it wouldn’t be the best. I’ll put my snorkel in my pocket it’s just to handy to leave at home.