Because I get so cold I wear a 5mm suit with a 3mm vest underneath. This requires a significant amount of weight to get and keep me down, about twice as much as I'd need wearing a 3mm shorty. On our 2nd dive I put my 14 pounds of weight around my waist and Phillip and I submerged. Well, I submerged, he was unable and had to return to the boat for extra weight. I felt too heavy, and was unable to add air to my BCD, causing me to panic just slightly, and to go up to get it fixed. Turns out, Phillip and I had taken each other's gear. His had ten pounds in the pockets giving me a total of 24. He had none. This is why the buddy check was invented!