My wife and I still practice buddy breathing. Long ago, I had a completely empty tank, not going into the long explanation and excuses, we were over 80 feet and I was minus zero PSI. It was before the octopus was in common usage, we buddy breathed from 80 feet up to about 50 or 60 feet where I left her and made a gentle ascent in no rush. I was very much needing air at the time my wife gave me her regulator at depth. I probably could have made it to the surface on my own but having her buddy breath with me replenished my body and allowed me to make a safe ascent in no hurry. N